Mainu is a fast-paced action adventure set inside a mysterious 13-floor mall consumed by energy. When Tonu meets a girl named Venera, he learns that a powerful being named Ormatsu has unknowingly infused his excess magic into ordinary capsule toys—creating living creatures called Mainus. Drawn to the mall’s endless flow of light, food, and movement, Ormatsu spreads through the building like a black hole, splitting himself into thirteen extensions that drain the life of each floor. Tonu’s own force energy allows him to control the awakened Mainus and fight back. Guided by Venera, he must collect, master, and unleash their power to stop Ormatsu before the entire mall—and reality itself—is consumed.

Tonu, like any other high schooler, has a dream to be an artist — but lately, he has stopped practicing his drawings and stopped believing in himself. One night, while sleeping, he meets a yokai named Ormatsu, the ruler of a realm called Ginga. To keep the realm alive, Ormatsu traps the dreams of people who give up and transforms their souls into dog-like creatures called Mainus. There is only one way to escape this world: solve the Ormatsu Puzzle and defeat him. Ormatsu gives each dreamer a chance to escape by collecting all the Mainus and mastering six elemental powers — Fire, Lightning, Water, Wood, Ice, and Wind — to defeat the fifteen rulers of the realm. Tonu has just eight hours in this dream state to complete the challenge, or he will be trapped in Ginga forever. Help Tonu defeat Ormatsu and reclaim his future.