Sekai Saionji (西園寺 世界)

Also in year 1, class 3, she is Makoto's classmate. Sitting next to him in class, she sees the picture that Makoto has secretly taken of Kotonoha on his mobile phone. She then helps him get close to Kotonoha despite harboring strong feelings for him. Even though she is good-natured her emotions overwhelm her in many situations. She lives with her mother in an apartment.

Known to be both a cheerful mood-maker and somewhat of a loudmouth. Her cute appearance and bright personality (as admired by Taisuke) attract a lot of secret fans, but with her frank and outspoken personality, all the boys who've confessed to her so far have been mercilessly rejected.

In the last episode,

Later on, she is invited by Kotonoha to go to the top of the school where Sekai tells Kotonoha that she is pregnant and it is revealed that Kotonoha had decapitated Makoto's corpse and was carrying his head in a duffel bag. Horrified, Sekai comes to the realization that Kotonoha was driven insane. Kotonoha asks Sekai if she can check if the latter is pregnant wherein she brandishes a hacksaw. Sekai attempts to defend herself with the same knife she used to kill Makoto, but is disarmed and fatally slashed across the neck. Kotonoha then proceeds to slice open her abdomen to check if she was indeed pregnant.

This is the last time Sekai appears in the anime.