Guy, a summoner, inherited his family heirloom: a coat with magic squares engraved on it. Sealed within it is a divine moon-beast, Sakim. Guy, who ended up without a single relative at a young age, became Sakim's master after making a contract with him, and now, they travel around together.

A bloodstained forest of wolves, a dark road where a will-o-wisp appears, a port town where something possesses Guy, and a swamp where ghosts spill forth – he relies on Sakim's powers for all of the mysteries he encounters on their journey. As compensation, he allows Sakim to sleep with him. Before they know it, Guy has closed his heart, as if he's been imprisoned by thorns…