Kokichi describes himself as an evil supreme leader. He is an elusive and manipulative person who unabashedly tells lies and says whatever he's thinking. He is also strangely straightforward about his supposed evil nature, openly claiming to be a leader of a large secret society, admitting to being a liar, and saying he has done nothing but bad things. Among other things, his organization supposedly has covert agents in every country, control over all the mafias in the world, torture as a form of punishment, and Kokichi's defeated opponents apparently will get sent in Siberia. However, none of his claims have been confirmed, and the other students think he's either lying or delusional. In his love hotel fantasy sequence, it's shown that he likes to view himself as a phantom thief type of a criminal.

According to Kazutaka Kodaka, Kokichi is a trickster character in the truest sense of the word.[6] He is very mischievous, and he enjoys pranks and teasing others sometimes in quite mean-spirited ways. Because of his behavior, he is viewed as an antagonistic figure among the group. However, even though people find him suspicious, he is still somehow able to manipulate the class trials. He is often portrayed smiling slyly and laughing mischievously, though he may look very harmless and innocent at first glance. He often behaves calmly and coolly in a way to torture the others, at times turning very ominous to the point of having very unsettling, downright demonic looking expressions. He can also try to use his looks to his advantage and sheds crocodile tears by crying loudly like a scared and threatened child, telling the others they're being really mean, but this is always overly dramatic and obviously fake. There are also moments when he suddenly falls asleep and snores comically, angering the others. He is well aware that he is disliked, claiming that nobody would care if he died.

Particularly, Kokichi considers lying a big part of himself and appears either unwilling or unable to stop it. He frequently claims something only to shortly afterwards reveal that he was just lying, making it very hard to trust his word. He also tends to say whatever riles up the other students at the moment and tries to mess up conversations without any apparent reason. Indeed, neither because of impulsivity or the need to confuse others, he lies mostly because he feels he's free to do whatever he wants whenever he wants. Being a liar himself, he sometimes seems to notice when and why other people are lying. He also appears to have little trust in anyone or anything, refusing to tell anything about himself besides his questionable supreme leader claims, and generally questioning the truthfulness of different situations. Ironically, he appears annoyed if other people are lying, either to others or themselves, and he claims that he hates liars.