Uuji, as he and Age search for their missing friend.
"to disappear second while going to search for Edo."
Uujima Satoshi is the most significant male in Irisu Syndrome and, arguably, the antagonist of the game. Both Irisu Kyouko and Age Hatori are romantically interested in him, and, out of this rivalry and Irisu's condition, stems the conflict. This article contains spoilers for throughout Irisu Syndrome.
Uuji has short blackish blue hair and dark blue eyes. He is seen throughout the game wearing mainly hoodies and jackets, with his arms in the pockets. It is noted that he only wears long sleeves, even during the summer. He states that he would be "estranged from [his friends]" if he didn't.
Uujima is a very quiet, secretive guy. He keeps his distance from others, and he is shown both looking down on loud, obnoxious people, as well as being a laughingstock of groups in class. He used to watch Irisu play with the school's bunny when they were children, and eventually fell in love with her. He would be very secretive about his visits to the bunny due to it being disliked by most of the students. He comes to find out Irisu was allergic to cats, and both were in different classes. Yet, he doesn't speak with her, first because he played with the cat often, stating that if he got too close to her 'she might have a coughing fit', later claiming he just didn't have the courage to do so.
One day on one of his secret visits to the bunny, he finds that it had passed away, due to natural causes. In order to not let the rabbit be forgotten in its passing, he decapitates it with a saw. He leaves the head inside of the cage and hides the body in a bush, the school staff states a dog had attacked the bunny. It's assumed Irisu was the first to discover the scene and was traumatized by it, her mental instability indirectly caused by Uujima.
He is portrayed to have a rather twisted mind, drawing cats committing suicide in any way that he can think up of, in his notebook. When he notices that his notebook has been secretly looked through by Irisu, he finds the situation pleasing, and continues to leave notebook after notebook for Irisu to look at. Pleased with the indirect relationship that they both have, his mind lapses into a state where he wouldn't mind being killed by her. Eventually, Uujima's idea of a "Happy End" is an end where Irisu kills him, along with the other friends. In an attempt to tempt Irisu into triggering this "Happy End", Uujima decides to draw tortured rabbits, as a sort of depraved "romantic gesture".
However, even so, Uujima is displayed having guilt for desecrating the rabbit's corpse, and is stated as regretting the fact that the rabbit had been so easily forgotten by anyone, believing that there should be some way that the rabbit should remembered by.