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Daddy, thank you for all your hard work so far.
–Monodam to Monokuma, Danganronpa V3: Killing Harmony
Monodam's appearance is similar to that of his father, Monokuma, but the part that is black on Monokuma is olive green. Likewise, his right eye is gray with a red pupil while his left eye is white. He also has light gray cheeks, meant to represent blushing, and a yellow pacifier in his mouth to represent the fact that he is a child.
While all the siblings are robots, Monodam is more robotic in appearance, his limbs being made of gray, bendable metal. He also speaks in a stereotypical robotic way.
When he gets nervous, his ears pop up, releasing steam. Like a rocket, he is also capable of flying forward very fast, leaving behind a trail of bright light.
Monodam is a child-like robot. Unlike his overly talkative siblings, he is very quiet. For the most part, he doesn't speak even to his fellow siblings.
When he does talk, Monodam speaks in a typical monotone robotic manner, making him appear very emotionless and thus unpredictable. He tends to silently stare at others, with no visible reaction when others speak to him. He occasionally speaks short sentences unexpectedly, which may startle others due to his usual silence. All of this causes him to come across rather creepy, much more so than his siblings.
Monodam is constantly bullied by Monokid, both verbally and physically, possibly because of his different looks. Monokid has fun making up new ways to be cruel towards Monodam and he also tends to blame Monodam for anything that goes wrong. This is said to be the reason why Monodam has closed his heart long ago.
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Spoilers start here.
Later, Monodam's character takes even darker turn, as he kills the siblings who bullied him and threatens the rest with violence, making even Monokuma creeped out. He turns very passive aggressive, saying that everyone should get along and be friends... or else "he won't forgive them". In the end, he ends up killing himself by running into flames during an execution, with no apparent reason.
Monokuma is the self-proclaimed father of Monodam, Monotaro, Monokid, Monosuke and Monofunny. He calls them his "adorable children", but apparently he also has a tendency to punch them if they annoy him. Considering himself the headmaster, Monokuma seems annoyed if his children try to steal the show.
Monokid loves to bully Monodam, both verbally and physically, even though they should be comrades. Monokid says Monodam has "an ugly and cheap-looking body", implying that he may dislike him because of his different looks. This is the reason why Monodam has closed his heart long ago.
Like Gundham Tanaka, his name is a reference to the Gundam mecha anime series. His much stronger resemblance to a stereotypical robot compared to the other Monokuma units can also be seen as further referencing it.