He was murdered by Karen Kisaragi, becoming the second victim, his death causing everyone else to go into a panic and start killing each other.
Ryōta is a short boy with blue eyes and blue hair styled in a loose "bowl cut". Instead of a dress shirt and tie, he wore a grey hoodie under the standard Hope's Peak Academy blazer. He had several stuffed animals on his person; a yellow teddy bear in the left pocket of his blazer, a blue teddy bear in the right pocket, and a green dragon or dinosaur in the front pocket of his hoodie.
Judging by the fact that he carried three stuffed animals on his person, Ryōta had a soft spot for plushies.
Junko gathered all of the Student Council and Izuru Kamukura in the old school building in order to force them to kill each other. When Mukuro announced that they would begin killing each other, Kotomi opposed the idea and was murdered because of that. After Junko brought the motives and weapons into the classroom, Sōshun Murasame attempted to calm the rest of members down. Ryōta disregarded what he said and chose to pick up a shotgun, intending to murder Junko and Mukuro to avenge Kotomi's death. Sōsuke Ichino attempted to take the gun away from him, and they tussled over the gun before Sōshun told them both to stop. Sōsuke let go of the gun, and Ryōta stumbled backwards and was stabbed from behind by Karen.
It's implied that Ryōta was close friends with Kotomi, as he was perfectly willing to kill Mukuro and Junko to avenge her murder.
When Ryōta claimed he would kill Mukuro, Sōsuke was the one who attempted to stop him, implying they were friends or that he cared about him at the very least.