The article below is based on non-localized content only available in Japanese.
As such, all information in this article is based on fan-contributed translations.
|“|| People are sheep. They are drawn to a name, and the school took advantage of that to get more money. Thanks to that, it went through a sudden growth spurt. We suddenly have research facilities that can make any university jealous. No one was prepared for that-- in just a year or two, Hope's Peak Academy grew to an entirely different scale.
Yasuke Matsuda (松田 夜助 Matsuda Yasuke), is a student in Hope's Peak Academy's Class 77-A featured in Danganronpa Zero. His title is Ultimate Neurologist (超高校級の「神経学者」chō kōkō kyū no “shinkei gakusha” lit. Super High School Level Neurologist).
Yasuke appears to be about 17 to 18 years old. 
He has a tall, slender and slightly lean figure, with that his face usually wears a signature apathetic gaze and this expression is more emphasized with his distinct, heavy-looking eyebrows that are usually furrowed. His face is also described as unhealthy-looking, supposedly because of stress, but he is mentioned by Monokuma to be “good-looking”. He has long-neck length messy black hair, which is mentioned to be silky and soft. His eyes are pale blue and he has long feminine eyelashes. He is described to have a somewhat pale complexion, long fingers, and thin, small lips.
On the account of his good looks, he is mentioned to be “popular with Reserve Course girls”.
Yasuke's attire consists of a half-tucked in, dirty white dress shirt and a sloppily worn black tie that is adorned with red decals. His lower-half consists of black trousers, a belt, and bathroom slippers.
Yasuke is referred to as a “sharp-tongued brainiac” by Monokuma's memo in his profile and he's described as good-looking and intelligent. However, he is also notably sarcastic, witty and displays a perpetual, disgruntled apathy. Despite his young age, he is a very skilled neurologist and is regarded as an expert neurosurgeon and neuroscientist. He also has a short temper and when he loses it, he can be quick to resort to a stinging and bitter demeanor. While being perfectly capable of being professionally-balanced and cordial, he is also capable of putting other people in their places if not downright scaring or intimidating them.
His attitude and general demeanor often cause him to butt heads with students and staff alike, but he's more prone to brushing off their complaints and arguments not too long after they start engaging in pointless lengthy disputes.
He is quite mean and rude, carries a dry sense of humor and an unapproachable, hostile attitude. He is aloof, enjoying spending time on his own and reading manga. He sees little to no point of respecting others without a good reason to do so and particularly because of this, he is notoriously known for standing up and having a complete disregard or dislike of authority figures. A prime example of this would be The Steering Committee, and how he was able to intimidate them by fearlessly standing up to them in an intense momentum of anger. His initial rudeness and callous demeanor can be seen especially towards Ryōko Otonashi, as he constantly calls her ugly and finds himself annoyed to a practically exaggerated level. However, in spite of this, he shows some concern towards her on account of her vulnerability and forgetfulness. He considers himself the only one allowed to make fun of her and he feels that he needs to speak up for her. According to Ryōko, he may be cold and blunt, but he doesn't treat her with fake sympathy.
Yasuke seems to dislike showing his feelings to other people and blocks others out by reacting in a stinging, unorthodox manner and this could be nonetheless contrasting to whether or not he's annoyed by loud and obnoxious people or he's just introverted and solitary. Yasuke exhibits behavior that gives off the impression that he's a loner, but it may depict him as more depressed and anxious than just anti-social. He finds it easier to do things underhandedly, as to not have his friends or acquaintances bother him about acting uncharacteristically kind. He tries as hard as he can to keep himself composed and calculating when faced with an obstacle in his path, no matter how anxious or uncomfortable he might actually feel. He seems to be quite emotionally distant and bitter, as Junko and his mother were the only close ones in his life and the process of having the two closest people to him put in unfortunate circumstances may have largely altered his emotional stability, starting with his mother whom he had to witness helplessly as she suffered and died of an illness that causes severe memory issues and followed by Junko, who was inflicted with a destructive obsession for despair.
Yasuke is also noted to be overly defendant of Junko, or rather her fabricated personality, Ryōko. This could possibly stem from the remainder of his mother as Ryōko, in the eyes of Yasuke, is quite similar to her on the account of her memory issues and appearance. While Yasuke appears to dislike killing and harming other people, as well as noted to hate gore, he is willing to sacrifice and risk himself and others for the sake of Junko, even if it causes him to suffer horrible guilt.
According to Yūto Kamishiro, Yasuke's neuroticism is very well known among his classmates in Class 77-A. He also appears anxious at times and doesn't care much about his looks. His shirt is constantly mentioned to be dirty, his hair remaining bed-headed and his eyes having bags underneath them.
Yasuke's talent as Ultimate Neurologist stems back to a traumatic incident in his childhood. When he was very young, his mother became sick and was later diagnosed with an unnamed neurological disorder, which would later cause her death. Before she died, however, her memory rapidly deteriorated, to the point where she would frequently forget who her own son was. Because of this traumatic time, Yasuke devoted himself to neurology in order to learn everything he could. As a result, he has a very broad knowledge of the complexities of the brain and most likely has a very complex understanding of human psychology. In charge of his own laboratory, he has an unlimited access to medicinal and clinical resources and is most likely trained in other specialties that involve medicine as well given that many neurologists also have additional training or interest in one area of neurology, such as stroke, epilepsy, neuromuscular, sleep medicine, pain management, or movement disorders.
Given that neurologists are physicians that have completed postgraduate training in neurology after graduation from medical school and finishing at least roughly 10–13 years of college education and clinical training, including obtaining a four-year undergraduate degree, a medical degree which comprises an additional four years of study, and then completing a one-year internship and a three-year residency in neurology, it is safe to assume that Yasuke's position as the Ultimate Neurologist and accomplishments at such a young age sets his medical knowledge not only limited to neurology but a variety of other medical specialties as well.
As an extension of his Ultimate Neurologist abilities, Yasuke's research led him to develop an experimental treatment that allowed him to repress a person's memories from a specific time period. It was thanks to this research (along with the efforts of Chihiro Fujisaki, Miaya Gekkogahara, and others) that the Neo World Program was able to come to fruition.
Yasuke is first seen using this technique on Junko, who he attempted to protect by modifying her memories and "hiding" her behind an alternate identity, Ryōko. During its experimental stages, Ryōko had to constantly receive "treatments" from Yasuke in order for the memory-erasure to not wear off. Unfortunately, it does, and Junko regains her memories, killing Yasuke in a fit of despair.
After his death, Junko steals Yasuke's research—which she would later perfect and use on the 78th Class in order to instigate the Killing School Life.
Yasuke is able to intimidate and scare others into listening or doing his bidding. As in such, he finds it quite simple to take advantage of situations that involve adversity, much like Byakuya Togami. His snide, cold and angry vibe contributes to him having the ability to put his dominance over others. He also possesses a profound, keen intellect and skillfulness at deceiving others all while remaining calm and collected through intense situations whereas others would usually panic.
Interestingly, Yasuke is quite skilled at handling scalpels as projectile weapons by using them like throwing knives, very much similar to Sonosuke Izayoi. It is often used as a tactic in the novel to frighten Ryōko several times.
In Yasuke's childhood, his mother was his only family. She was diagnosed with an unnamed disease that appeared to have symptoms similar to Alzheimer's disease, causing her to forget who her own son was. His mother's doctors also forbade Yasuke from addressing her as “mom” or “mother” and he was subjected to neglect, abuse and being treated as a stranger by his parent because of her constant memory loss. It's implied that all of this made him ambivalent, distant and majorly depressed, which is probably the reason why he didn't have any friends.
The mother's condition eventually led to her unfortunate death. Although Yasuke claimed that her death lifted a weight off his shoulders and made him "free", it is heavily implied that he continued to harbor a large amount of guilt and grief over her demise. Her death may also be responsible for his profession in the field of neurology, due to the bitterness felt on his behalf towards her doctors, who could have done better in his eyes.
During elementary school, Yasuke befriended Junko. Both of them didn't have any other friends and she was the closest person to him besides his mother. One day, Junko began working on a sand sculpture based on the Sagrada Familia church. However, a month later, it was destroyed by an unknown culprit. After seeing her break down in tears and weep for almost a whole day, Yasuke decided to go and search for the perpetrator. Yasuke's investigation eventually wound up to a dead-end, as he had never found any witnesses. Not being able to find out anything useful discouraged him. While he was sitting on a bench in front of the remains of the sand sculpture, Junko ran up to him with a large smile and whispered in his ear that she was the culprit who destroyed the sculpture all along, asking him to keep it a secret. When asked for a reason, she replied that she did so by accident. Truthfully, she had done this to get Yasuke out of his house, upset that his mother's condition had led him to become more withdrawn than usual.
In the years following the death of Yasuke's mother, Junko became the person that Yasuke felt he could always lean on, in fact, he didn't have any other close ones. She promised to always be there for him, which helped develop his stronger feelings towards her. She said she'll never forget Yasuke even if she forgets everything else, and that they'll always be together. For the first time in his life, Yasuke cried in front of another person, after making her promise she won't make fun of him, won't tell anyone and won't try to console him.
Shortly after his mother's demise, Yasuke began studying medicine. On his own and at a young age, he managed to become an expert physician and a full-fledged neurologist before even graduating from middle school. By the time he reached high school, he was quickly scouted to enroll into Hope's Peak. Despite the title given to him by the academy and because of his academic devotion to medicine, he was also regarded as an expert neurosurgeon and neuroscientist, with members of the school's staff acknowledging his skill and expertise. Because of this, he was often asked to run errands for the faculty or help with specific tasks they couldn't handle on their own, later being rewarded for his contributions by being granted his own laboratory in the school's dedicated Biology building and control of the aforementioned building's Neuroscience Institute in Hope's Peak Academy's eastern quarter. He was enrolled into Class 77-A, while Junko was a member of the 78th Class.
After the Tragedy of Hope's Peak Academy, Yasuke was the only student the facility trusted with the secret of their cover-up, as they needed his neurology skills for extracting and covering information from people. In exchange for his cooperation, he was awarded a large research grant and equipment for his lab.
Due to his incredible skill in neurology, Yasuke was requested by the school to assist in interrogating Junko about the incident. However, in reality, he was on Junko's side and reluctantly helped her. Junko had her memories wiped out for the purpose of testing the memory-deletion procedure meant to host Class 78th's Mutual Killing Game, as well as to hide from suspicion. She assumed the false identity of Ryōko Otonashi and became Yasuke's research subject. In good intention, to protect her from herself and to protect other people from her, Yasuke attempted to foil Junko's plans by preventing her from regaining her memories. He gave her "treatment" regularly, though, in reality, he was making sure that her condition stayed the same.
A month after the Tragedy of Hope's Peak Academy, Ryōko once again goes to see Yasuke for her treatment.
Yasuke throws a scalpel towards Ryōko and repeatedly insults her by calling her ugly. He then asks her who she is, claiming that he doesn’t know because he keeps looking at his manga. Ryōko answers the questions and Yasuke is surprised to find out that she remembers what just happened and what they talked, meaning that her condition might be better or maybe worse.
Yasuke gives Ryōko her treatment. Ryōko is shocked when she is reminded that she was almost suspended from school due to her bad grades, especially because it would mean she would be apart from Yasuke. Yasuke tells her he defended her because she is too valuable research subject to lose. They talk more about Ryōko's condition. Ryōko claims she isn't worried about it, and that she’s more worried about being cured because she wouldn’t get to see Yasuke anymore. Darkly, Yasuke tells her he won’t let her treatment end.
As they hear a noise outside, Yasuke explains to Ryōko about the reserve course students. He leaves to see the Steering Committee, while Ryōko sleeps in the lab.
Jin Kirigiri and the Steering Committee greet Yasuke. The Steering Committee asks Yasuke to extract information from Sōshun, the second survivor of the school's Tragedy who is currently in a coma. Yasuke is angered when the Steering Committee talks about Ryōko in an insulting manner, but Jin calms down the situation and they come to an agreement.
Yasuke returns to the lab and wakes Ryōko up roughly. He throws her out and tells her to come back in three days.
On the dawn, Yasuke learns that Ryōko has gone missing. He looks all over for her, only to find her sleeping on his lab's bed. He ties her to the bed, to make sure she won't wander off again and she can reflect on what she did. When Ryōko refers to herself as his lover, Yasuke tells her he wouldn't have such a vermin as a girlfriend.
Angry, Yasuke lies under the bed, but he then turns silent. He sighs and says that Ryōko has always been that way and she knows the perfect ways to irritate him, referring to Junko. He tells her how in their childhood she destroyed her own sand-castle, and after hearing the frustrating story, Ryōko agrees she should be tied up. She is angry that she can't write the story in her notebook, though, but finds out it's next to her pillow. As she struggles to open it, she reads the sentence "It seems Junko Enoshima killed him —" and mention of a dead body at the central plaza. Ryōko panics about the dead body, but Yasuke doesn't seem to care about it and instead asks her if she knows who Junko Enoshima is, which confuses her. Ryōko tries to ask him if Junko is his friend, but Yasuke avoids the question and tells her that there is no body.
Ryōko can no longer reach the notebook and Yasuke tells her that Junko has nothing to do with them and she should forget about it and that all of it was probably just stories she made up. Ryōko says she would never do that because it would confuse her true memories, but Yasuke claims she must be very lonely due to her memory loss and she creates delusional stories for that reason. Frustrated about how badly she is misunderstood, Ryōko screams loudly that she is never lonely as long as she has Yasuke. She asks how he can forget that if she can remember it despite her forgetfulness. Yasuke wants to end the conversation and assures her that the notebook lies and she can believe in him instead.
Ryōko is conflicted, as the notebook and Yasuke are two the most important things to her. She decides to believe in Yasuke instead of in herself and tells him that she will give away her memories if he always stays by her side. Yasuke stays quiet for a while and answers it's impossible right now because he has other things to do. Ryōko says that his research is most important to him and he will never choose her. Yasuke says it's not it, but turns silent again. Ryōko begins to cry and asks him to at least cure her or make her forget him along with everything else, so she wouldn't feel so painful. Yasuke stands up quietly and wipes her face gently with a tissue while looking at her with lonely eyes. For some reason, Ryōko feels fear.
Silently, Yasuke turns to leave and tells her he has an appointment with another student, and that they can continue talking after he returns. After he returns, Ryōko hugs him happily as she doesn't remember their previous conversation anymore. Nevertheless, Yasuke bashfully tells her that he's sorry and unusually lets her hug him. Then, he asks how she's untied, but she can't remember anymore. As she continues to cling on Yasuke, he whispers that the reserve course students' Parade is growing louder outside. Reluctantly, Ryōko leaves back to her room.
At the east compound of the school, the school's doctor guides Yasuke to see Sōshun Murasame. Yasuke asks to go alone and sees the other boy in a comatose-like state, unresponsive to his questions.
Yasuke keeps talking to Sōshun and the other boy is revealed to be conscious, though nevertheless largely unresponsive. When Yasuke asks about Izuru Kamukura, Sōshun claims he killed the student council. When he asks about Junko Enoshima, Sōshun's behavior changes completely. Yasuke watches "Sōshun Murasame" stop existing in front of him, as he appears to turn completely mad, wildly screaming about Junko Enoshima and killing her.
Yasuke realizes he must protect Junko no matter the cost, even if it would cause him guilt and grudge against himself. To protect Junko and stop information about her involvement in the incident spreading, Yasuke decides to kill Sōshun and strangles to death the other boy who appears defenseless and unaware of what is happening.
Sweating and anxious from the murder he committed, Yasuke tries to go see Ryōko, but she isn't in her room. He then goes to his lab and finds it has been a victim of vandalism. He sees a girl hiding under the bed, but it turns out to be Junko. They talk and Junko asks him what he is going to do now, claiming that she isn't doing anything and not seeming to be worried about the outcome. She ends the conversation with a kiss, but Yasuke turns numb and immobile as a result. Junko explains her lipstick was tainted with poison, but she also says it isn't life-threatening. Before leaving, she tells Yasuke that only he can make the choice concerning their situation. After this, Yasuke disappears, as other people cannot find him.
Yasuke appears inside the old school building, in Izuru Kamukura's hiding place. He kills Yūto who was investigating in the room with Ryōko. He appears to feel bad for him, saying that maybe he would've been spared from such a fate if he didn't meddle with Junko Enoshima's affairs.
Ryōko doesn't recognize him and asks who he is. Yasuke is surprised and looks completely exhausted. Coldly, he asks why doesn't she remember him. Ryōko tries to explain that she easily forgets things, but she suddenly feels pain in her mind, as her original persona slowly begins to merge. Yasuke claims to be Izuru to test her memory and looks at her with sad eyes. Ryōko feels a bit afraid of him.
Yasuke says he has decided to talk a bit before he makes his decision. He explains that The Tragedy of Hope's Peak Academy didn't mean much for Junko, as her true goal was to brainwash the reserve course students. He says that Junko used him and the student council as sacrifices solely for that purpose. Yasuke says he didn't want to believe that she was so obsessed with despair, that he was only controlled for that purpose, and that he is involved in the incident. Yasuke then stares at Ryōko with a deadly hatred, assuming that she has remembered that he wasn't a particularly important person to her, which made her forget him. Ryōko finally realizes that he isn't Izuru and angrily he tells her that he is Yasuke.
Yasuke tells Ryōko that Izuru has been taken away a long time ago. Ryōko is surprised that he is Yasuke, because she doesn't feel her usual feelings for him, but she confirms it with her notebook and the way he speaks. Yasuke says that she has stopped thinking about him because she has begun to remember other things. He says that his existence was never special to her and she only assumed that because she had forgotten that fact. Ryōko is confused, but then she begins to remember why she wanted to see Yasuke and how she used to act towards him. Unable to believe in anything, she begins stepping back and the wall blocks her way. Yasuke moves towards her and she feels afraid.
Ryōko tries to tell him that they should go back to how things were, but he says it's already too late and they can't go back. With a sad face, Yasuke explains that the school's tragedy made him realize that his life was just a fake scenario set up to control him. He was completely fooled by Junko, but he thought he could save her and stop her. In order to protect her, he concealed her existence itself. Regardless, she had the Steering Committee murdered, and Yasuke hid the corpses and dealt with the evidence for her sake. He confesses that he even murdered for her sake. Ryōko asks if she's that important to him and he answers that she is. Yasuke explains that the reason for that is the fact that she prevented him from being all alone after he lost his mother. She became the most important to him, even though he says she's not a lover, family nor even a friend.
When she hears how Yasuke feels about Junko, Ryōko believes she has no chance of competing with her. She lets out a deep breath and Ryōko's persona appears to begin to fade away. Suddenly, Mukuro disguised as Junko appears, saying that she just came to provide the supplementary explanation. Ryōko remembers Mukuro's face and Mukuro explain she has just been following Junko's orders. Yasuke understands that Junko anticipated his actions and he angrily says that she is now spectating his actions in amusement. Ryōko is confused by their words and is already incapable of understanding Yasuke's feelings. However, she understands that he both loves and hates Junko. Ryōko realizes that she can only give up and let her and Yasuke's world end.
Yasuke lets out a huge sigh and then, eyes brimming with determination, says that he must end this. He says that his desire to protect Junko was likely true despair and his despair won't end unless he ends this. He says he desperately tried to hide her and not have her involved with others, thinking he could protect her. However, it was pointless, as his actions meant nothing to Junko. In the end, she could only inflict despair on anyone involved with her. He says it's despair that he finally understands this.
Deciding to end everything, Yasuke attempts to strangle Ryōko to death, saying that it's for his and not Junko's sake. Once again, Ryōko hallucinates, seeing and hearing Junko's figure. As she imagines Junko's face, she finally remembers that it is her own face. At that very moment, "Ryōko Otonashi" stopped existing, replaced by her original persona. Junko laughs, saying that Ryōko never existed in the first place.
Suddenly, Junko stabs Yasuke in the side with a knife. Quickly dying from the wound, Yasuke tells her that he lied to her and that his "treatment" had prevented her from remembering. However, Junko already knows this. Yasuke asks her why she pulled the whole turn of events, assuming that she wanted to pull him into despair, as he was the one who always thought of her. Junko gently caresses his face, but then denies his words angrily and pulls her hand away. Yasuke collapses in the pool of his own blood, realizing that Junko truly doesn't care about him. Before his death, Junko bluffs that it was her who was responsible for the death of his mother, however, it's unknown if she was actually responsible or just said this to pit Yasuke further into despair during his final moments. Junko refuses to answer him and he dies with never knowing the truth.
After Yasuke's death, Junko lets out her true feelings and feels sadness, as he was the most important to her of all. She kicks his body until it's a bloody unrecognizable mess, laughing and crying, as she feels the incredibly strong despair of murdering her loved one.
Yasuke appears as a cameo in the OVA, was shown with Ryōko and Isshiki.
Yasuke's mother is said to be the closest person to him aside from Junko. It is assumed that his relationship with his mother before her disease was peaceful, however, it was severely strained after she was diagnosed with a fatal illness that is implied to be Alzheimer's disease. The symptoms included long-term memory loss which resulted in her not being able to recognize her own son and being thrown into hysteria which led to possible abuse and neglect on her own son. After she passed away, Yasuke was thrown into a pit of depression and grief.
He often displays traits signifying that he holds grief and bitterness towards the doctors who in his eyes, could've done a better job of saving her life. It is most likely this traumatic event in his childhood that led him to pursue into the field of neurology to which he excelled at.
Junko is Yasuke's childhood friend, as well as the closest person to him besides his own mother.
They became friends during elementary school and neither of them had any other friends. One day, Junko began working on a sand sculpture based on the Sagrada Familia church. However, a month later, it was destroyed by an unknown culprit. After seeing her break down in tears and weep for almost a whole day, Yasuke decided to go and search for the perpetrator. Yasuke's investigation eventually wound up to a dead-end, as he had never found any witnesses. Not being able to find out anything useful discouraged him. While he was sitting on a bench in front of the remains of the sand sculpture, Junko ran up to him with a large smile and whispered in his ear that she was the culprit who destroyed the sculpture all along, asking him to keep it a secret. When asked for a reason, she replied that she did so by accident. Truthfully, she had done this to get Yasuke out of his house, upset that his mother's condition had led him to become more withdrawn than usual.
In the years following the death of Yasuke's mother, Junko became the person that Yasuke felt he could always lean on. In fact, he didn't feel close to any other people. She promised to always be there for him, which helped develop his stronger feelings towards her. She said she'll never forget Yasuke even if she forgets everything else, and that they'll always be together. For the first time in his life, Yasuke cried in front of another person, after making her promise she won't make fun of him, won't tell anyone and won't try to console him. He became dependent on her and ready to do anything for her, because she told him she'll be what's important to him for now and prevented him from being all alone when he needed it the most. Junko also had a tendency to call them "lovers" and had romantic feelings for Yasuke, but he denied this with annoyance and called her a "stalker", treating her very similarly like he does Ryōko later in life. Yasuke has described Junko as "not family, a lover or even a friend ... but someone just as important to (him) as any of those".
Both of them later enrolled in Hope's Peak Academy and after the school's tragedy, Yasuke reluctantly assisted Junko in her plans, creating her alternative identity Ryōko Otonashi. He wanted to prevent her from ever remembering, in order to protect her from herself and to protect other people. However, Junko had already planned ahead and had murders occur in the school. Despite not enjoying despair and killing, Yasuke was willing to do bad things for the sake of protecting Junko, even if it caused him to feel horrible guilt.
Their relationship appears to be characterized by twisted unethical doings, unhinged devotion and protection – although unfortunately, Yasuke, with his morality going down the drain was in for a downfall despite things seeming hopeful when it came to the Sōshun Murasame, The Steering Committee and others being silenced for the sake of Junko being shielded from the spotlight. Yasuke demonstrates an absolute loyalty and willingness to pull through chaotic, immoral and frightening situations in order to protect her to a self-destructive point. He seems to realize exactly how toxic and corruptive the inner-workings of his relationship with Junko is, but amidst his cynical and pessimistic view of the world, he is certainly optimistic that he will succeed in saving her from her herself and preventing any more tragedy.
Finally, Yasuke understands and admits to himself that Junko has only been using him. He is frustrated by her love for despair and he's angered when he comes to the conclusion that she never cared about him. He states that he both loves and hates her, and eventually he decides to kill her when she is still Ryōko. However, he ends up getting killed by Junko in a fit of despair, as he is one of the people she cares about the most. He was stabbed in the abdomen by Junko and afterward she kicked his body until it was rendered mutilated and unrecognizable. He died believing that Junko did not care about him at all, but in truth, this was not the case. Junko felt painful grief for his death and let him die in despair for the sake of increasing her own despair.
Ryōko is the alternative, amnesiac identity of Junko. Even though she has constant memory issues, she is still in love with Yasuke.
From the beginning, Yasuke treats her condescendingly, berates her, and often makes fun of her whenever he has a chance to. On the other hand, Ryōko is infatuated with him and holds a deep liking towards him despite his sharp tongue. She acts clingy when she is around him and constantly whines when he's present. It's stated that she likes Yasuke, because he doesn't treat her with fake sympathy. There are times when Yasuke is shown to warm up towards Ryōko, even appearing gentle towards her when she cries about her painful situation. At one point, he ultimately apologized for getting angry.
On the note of her amnesia and treatment, Yasuke is shown to be, if not intensely protective of Ryōko, then quite defensive for her. This is shown when one of the old men of the Steering Committee insults Ryōko for being a “dunce with no hope of recovery” and reckons her to be a failure. This causes Yasuke to respond in contempt, yelling at one of the committee members to “shut the fuck up” and that his “dirty mouth talks too much”. He proclaims that he is the only one allowed to make fun of Ryōko.
During his untimely end, Yasuke is revealed to have been protecting Junko's alternate identity, Ryōko from herself by planting fake information inside of her notebook. He even attempted to kill Ryōko before she regained her memories. However, this failed miserably when she fell into a fit of despair and killed him after realizing who she truly was. The motive for her murder was simply the desire to drive herself further into despair by killing one of the two people she loved the most: Yasuke and Mukuro Ikusaba, whom Junko later kills during the killing game of Class 78.
It has been stated that Ryōko especially is very similar to Yasuke's mother concerning her appearance and memory issues, which might be one of the reasons why he's fond of her.
They are fellow prominent collaborators in creation of the Neo World Program.
- “I just did some calculations and I've been able to determine that you're full of shit.”
- “You're also too loud for someone as ugly as you. Speaking of, someone as ugly as you being scared of flying scalpels is weird too.”
- “Shut the fuck up, old man. Your dirty mouth talks too much.” (to The Steering Committee)
- “Honestly, your brain is like a bottomless bucket.”
- “Who are you going to report me to? The National Japanese Ugly People Association? That kind of organization would be guilty of discrimination just by existing.”
- “You don't often see someone possessing such a superb, brain-intensive talent as you do affected by memory loss. That's why you're such a rare case.”
- “Saving the people you love isn't stupid. It isn't even a choice.”
- “You’d be surprised to know how little Hope's Peak cares about what is and isn't morally justifiable. As long as we've got talent, we can do pretty much anything we want. It's a tragedy, but I don't think I need to remind you that these are the same people that scammed a bunch of families into sending their kids into some random private high school near the academy.” (to Ryōko Otonashi)
- “In order to understand what triggers amnesia, we need to find the molecular mechanism that it’s connected to. Once we find that, our understanding of memory will improve a tenfold. We’ll be able to create medications to improve memory. Then, maybe in the future, we’ll be able to even store backups of our memories on hard drives… if it’s possible to create that sort of system. Actually, there are studies delving into that currently in foreign countries. By suppressing Protein kinase M zeta, it’s been found it’s possible to erase a lab rat’s long term memory.” (to Ryōko)
- “Still, in the future you should talk to an expert about it. But, if you can't do that, come to me. That's all there is to it, right?”
- “You say clarify the truth, but aren’t you trying to cover it up? Isn’t that just a contradiction?” (to Jin Kirigiri)
- “Yasuke” (夜助) is composed of 夜 - “evening” or “night” and 助 - meaning “help” or “rescue” which most likely refers to the fact that he attempted to protect Junko Enoshima from being caught as the mastermind and all the while as he attempted to keep her from regaining her memories for the purpose of preventing the following events of Danganronpa: Trigger Happy Havoc.
- “Matsuda” (松田) translates to “rice field of pine”.
- According to dialogue between the two, Ryōko had bugged Yasuke to watch the movie Home Alone starring Macaulay Culkin for some time, yet always mistakenly referred to him as "Wacoal Culkin". Wacoal is a manufacturer of women's lingerie and underwear, founded in 1949 in Japan by Koichi Tsukamoto.
- He mentions that he dislikes gore.
- Yasuke likes reading manga.
- Yasuke was referenced in one of the Nonstop Debates in the last Class Trial of Danganronpa 2: Goodbye Despair, "Wh*re's Yasuk=?". Interestingly it appeared after Alter Ego Junko revealed Hajime Hinata's true identity as Izuru Kamukura.
- Though not mentioned by name, during Junko Enoshima's Winter seasonal event with Mukuro Ikusaba in Danganronpa V3: Killing Harmony's Ultimate Talent Development Plan, Junko mentions how boring it was to watch her "childhood friend" (Yasuke)'s graduation and how boring it was that he seemed so happy.