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Tear Jerker: Kyoukai no Kanata
Mirai and Ahikito's fight. The one person to treat her like a human being runs the risk of permanently becoming an immortal rage monster and she has to kill him before this happens. The scene is Deliberately Monochrome and she has flashbacks to her most cherished moments with him before finally delivering the fatal blow.
Episode 0 has a brief shot of an extensive first aid kit and several strips of bloody bandages in the derelict house Akihito resides in, alluding to just how many people have hurt or tried to kill him in ignorance of his human emotions.