Buddy Collection Extra: Kochousou no Kimyou na Go-nin

The protagonist (Nagisa) is a high school girl who lost her memory and Buddy in the middle of an operation. She was originally a Special A Class student, but was demoted to an E Class student, which is the lowest possible rank class. E Class is a gathering of problem children who cannot make Buddies with anyone. In order to choose a new Buddy from among them, a camping trip is held. However, an incident occurs during the trip—.