Yuri has just been awakened after recovering from an attack by Gnosia infectees; humans infected by an alien organism that causes them to kill others. As their refugee ship from Liu-An is threatened by the detection of a single infectee amongst them, Yuri (affected with amnesia)...

On her way cycling to school, a long-haired stranger stops Suzume to ask if there were ruins nearby. After letting him know, she suddenly has a feeling they've met before and decides to follow after him to the ruins. She doesn't find her there but instead, she finds a white door...