A what-if scenario following Goro Akechi's disappearance in Persona 5, the charismatic ace detective and cold-blooded assassin winds up in Gensokyo, where he must reinvent himself, make new friends and allies, and confront a force which threatens to drown humans and youkai alike in their worst instincts.

One day, in the skies above Gensokyo, an Ultra Wormhole appears, which Reimu goes to investigate. What follows is an adventure that will tie the fates of two lands together forever, and reveal some startling truths about Gensokyo's past.