Kokichi Ouma (Kokichi Oma in the English version) is an antagonist turned anti-hero of Danganronpa V3: Killing Harmony. He is titled the Ultimate Supreme Leader.
After he successfully participated in the 53rd Killing Game, Kokichi's memories and past were fabricated by Team Danganronpa as follows: Kokichi's past is very unclear due to his constant lying and the fact that he strictly refuses to reveal anything personal about himself. In fact, the only thing known about his life for sure is his love of video games and that he's been playing them his whole life. However, he has also claimed that nobody would care if he was gone, and it's been implied that he has no parents or family.
It's known that he is the leader of D.I.C.E., a small group of young pranksters, who are the most important people and like a family to him. They have traveled around the world and commit "laughable crimes" for fun, which could indicate that they could be a group of orphans with no families nor parents to hold them back. Kokichi is also good at stealing, which might be due to his past, and it has been pointed out that many of his skills have a resemblance to a petty thief. Furthermore, his organization could be a reference to the animated television series D.I.C.E. (DNA Integrated Cybernetic Enterprises), which is about an organization run by children, specifically orphans. During the killing game, Kokichi lies that he is the supreme leader of a large, evil secret society. Obviously, there is no evidence of it and the Ultimate Detective, Shuichi Saihara, does not know any organization matching with the one Kokichi mentioned. During his Free Time Event with Shuichi, Kokichi claims he became the supreme leader by killing his parents and taking their place. He then claims he lied, and that the one he killed was his older brother. He claims he lied again and that the real reason is a secret. Considering his tendency to have some truth among his lies, this could imply something about his past.
There is a scene in the bonus mode Ultimate Talent Development Plan which hints about his family situation, as Kokichi and Kaito won't go home for New Year's, Kaito due to his unconventional family situation of living with his grandparents. Kaito asks Kokichi why he isn't at home with his parents (and aren't his parents embarrassed of him being such a brat at his age). Kokichi only tells him that he shouldn't ask such personal questions when talking to the supreme leader.
However, it is unclear how much, if any of Kokichi's past before participating in the 53rd Killing Game was real, and which was fabricated by Team Danganronpa.
He claims to be the mastermind of the Killing Game although it’s later revealed he was trying to deceive everyone to end the Killing Game. He is killed by Kaito Momota as of Chapter 5. He is the supreme leader of an organization named D.I.C.E. Though he calls himself ‘The Ultimate Supreme Leader of Evil’ the organization was actually just a group of pranksters who committed ‘laughable crimes’.
Described by Shuichi Saihara as "the human embodiment of a lie", Kokichi is a masterful schemer who enjoys creating lies and freely states whatever he's thinking, regardless of how it makes others feel. He often says things in an attempt to anger the others, such as constantly teasing Keebo and Miu and calling Maki a nerd for knowing a lot about killing. Because of this, Kokichi is easily capable of manipulating the class trials, often leading the others into dead ends or in an attempt to intimidate the culprit.
After the conclusion of the fourth class trial, Kokichi pretends to mourn for the now deceased Gonta, only to reveal it as a lie soon after and state that he'd never cry for him. From this point onward, Kokichi's mischevious and somewhat childlike demeanor is dropped, with Kokichi now acting cold, uncaring and nearly insane. He claims to enjoy the suffering and pain of others, with the Killing Game serving as a perfect source of it.
In spite of Kokichi's antagonistic nature on the surface, as well as his various cruel deeds throughout the game, Kokichi does indeed possess a compasionate side; albeit one that is rarely seen by the other students. During his private conversation with Kaito in Chapter 5, Kokichi expresses his true feelings towards the Killing Game, stating that those who are enjoying the students' suffering "piss him off" and that he had to "lie to himself" in order to get any enjoyment out of it. Kokichi considers lying to be a major part of who he is, believing lies to be just as - if not more - important than the truth. He also claims to use them as a way to entertain those around him.
Kokichi Oma at the Villains Wiki.