Makoto and Kotonoha walk around town together, while Sekai is still at Makoto’s house, waiting for him to come to dinner. As the two eat out at a restaurant, Sekai calls Makoto. She wants him to come home, but when he refuses, she wants to know who he’s with, accusing him of cheating on her (Bitch, you have no room to talk. Your entire relationship is based on cheating.). She tells him to take some responsibility, because his child is inside her, and he absentmindedly says that Kotonoha would never say anything like that. He tells her to go home and stop trying to act like his girlfriend.
Makoto and Kotonoha go back to Makoto’s place. As Makoto goes into the kitchen to make tea, he sees a huge mess on the floor. Apparently, Sekai had a tantrum and threw all the dinner onto the floor before leaving. Sekai, who caught a glimpse of them passing by on the train beforehand, heads to Makoto’s place. She’s pissed.
Kotonoha answers the door and is immediately slapped by Sekai. She accuses her of seducing Makoto into inviting her over. Kotonoha calmly, quietly reminds Sekai that she was the one who seduced Makoto. She’s seen through all the bullshit that not only Sekai, but Setsuna too, put her and Makoto through, and she’s done.
Kotonoha has forgiven Makoto, and she’s forgiven Sekai. She’s ready to live happily with Makoto, and delivers one final “fuck you” to Sekai by kissing Makoto. Kotonoha goes home later that night.
The next day, Makoto texts Sekai. She’s elated, until she reads the text. It’s regarding an abortion clinic that a friend of Kotonoha’s family runs. She’s absent at school. At noon, Makoto and Kotonoha eat lunch on the roof, like old times. He finally apologizes to her for everything.
After school, Sekai comes to Makoto’s house to talk. The two are silent for a long while, until Makoto volunteers to make tea. Sekai gets up to do it first. She sees the dinner she cooked in the trash, and texts Makoto. He gets up to get his phone in his room. As he reads the text, she sneaks up and stabs him to death with a knife from the kitchen.
She runs off when she realizes what she’s done.
Kotonoha arrives later to find Makoto dead on the floor in a pool of blood.
Then she starts pulling some Lelouch Lamperouge shit: She texts Sekai from Makoto’s phone, arranging for them to meet on the roof of the school. Sekai arrives with her knife, thinking she knows what’s up, only to find a duffel bag on the bench. Kotonoha comes out of nowhere, asking if she went to the abortion clinic. When Sekai tells her she didn’t go, she accuses Sekai of lying to try and keep Makoto to herself. Sekai denies, but Kotonoha then asks why she didn’t bother to prove it to him at the hospital.
Sekai says she endured everything for Makoto. Kotonoha then directs her to the duffel bag. Warily, Sekai opens it. We’re to assume Makoto’s head is in there. Kotonoha then offers to confirm if Sekai is really pregnant, brandishing a bloody backsaw, evidently the tool used to remove Makoto’s head. Sekai pulls her knife, but Kotonoha uses her ninja skills to disarm her and leave her defenseless. She slices Sekai’s neck open.
Immediately afterward, she slices open Sekai’s belly. It turns out Sekai was lying.
The last we see of Kotonoha is her sailing on her family’s yacht, cradling Makoto’s severed head.