The stage 6 boss, Byakuren has said that she was once a human and worked with her younger brother as a monk. When he died, she feared death, but she was able to maintain her youth with her power. However, she feared that she might lose her power, so she helped youkai in many ways. But she didn't hate humans either, because she wanted humans and youkai to co-exist. She was ultimately sealed away in Makai by humans. During the events of Undefined Fantastic Object, the youkai she has saved reappear to break her free from the seal. Her fate depends on which heroine is chosen by the player.
Based on events in Undefined Fantastic Object's Extra and later on in Touhou Hisoutensoku, she made a temple near the Human Village.