Reisen is a lunar rabbit who fled from the moon to Gensokyo early in the events of Touhou Bugetsushou. She was nursed by Reimu after being injured by space debris.
Reisen Udongein Inaba is her real name and she is a character from Touhou Project pc games.
During the Imperishable night (8th series of the game), she hid herself with Eientei on earth in order to avoid being sent back to the moon by lunar emissaries.
Reisen’s power of insanity comes from her eyes; she uses them to refract and twist waves, disorienting and confusing her victims and deceiving them with frightening illusions.