Giboura Massacre

Giboura Massacre also known as The Giboura Junior High Mass Murder Case, is an event featured in ''Danganronpa Gaiden: Killer Killer. ''

It was a mass murder performed by Hope's Peak Academy's Ultimate Soldier, Mukuro Ikusaba, who was ordered to do so by her younger twin sister, Junko Enoshima, also known as the True Ultimate Despair.

It takes place before The Tragedy and also the only event in the series that isn't part of the main story's timeline.

Prelude
Soon after Mukuro arrived in Japan, Junko, who was worried if her older sister's talent as the Ultimate Soldier became obsolete, planned to test her talent by planning a mass murder. She picked Giboura Junior High and ordered Mukuro to go on murder rampage there.

The Incident
The incident took years before The Tragedy in a Junior High School where Takumi Hijirihara attended school. Takumi became best friends with Shūji Fujigawa during Junior High. Takumi, along with Shūji are two of the students that witnessed the murders in junior high school that left Takumi scarred and began his disturbing obsession with murder, which he takes out on other killers. They were survivors that were spared. Takumi promised that one day he will become the best killer and surpass the Ultimate Soldier.

While the event turned the shy and timid Takumi into a lover of passionate killings, the massacre also affected Shūji greatly. The Giboura Massacre completely breaks Shūji's calm demeanour, to the point that he turns into a zealot to stop all serial killings.