Mount Taketori Incident

The Mount Taketori Incident (竹取山遭難事件) was an event that happened 7 years before the start of the story that happened on Mount Taketori, where a group of four elementary school students were involved in an incident where three of them fell seemingly to their deaths, leaving the one survivor, Chuuta Kokonose, behind. It was also classified as a space incident.

Breakdown of Events
During a class field trip to Mount Taketori, a group of friends (Chuuta Kokonose, Ken "Gucchi" Mizoguchi, Matsutarou, and Michiyo), decided to break away from their class to go to the top of the mountain. While they were walking near a ledge, the ground suddenly crumbled beneath their feet. Matsutarou almost fell but Gucchi and Michiyo managed to hang on to him. All three shout for Chuuta to help them. As Chuuta tried to reach them, the voice in his head tried to warn him about the unstable rocks, but he accidentally stepped on them, causing his friends to fall to their deaths. However, their bodies were never found.