The peaceful Maynou Kingdom was destroyed by a sudden invasion from the Perigia Empire. Yoru Maynou, the prince of Maynou and a magical genius, was mercilessly exploited as a "battery," his magic power squeezed dry to fuel the empire's prosperity. Finally reaching his absolute limit, his magic power ran out, and he breathed his last.However, in the threshold between life and death, Yoru was guided to "Avalon's Gate," a realm where legendary heroes gather. There, in order to fulfill a promise to his beloved younger sister Noel, he proposes a deal to the heroes: lend him their strength in exchange for regaining their lives.The intrigued heroes accept the bet, allowing Yoru to make a miraculous return to the living. Now, the former genius magician wields the overwhelming martial might of the real-world heroes he has summoned, such as Okita Soji and Joan of Arc.This is his grand tale of revenge as he leads the strongest heroes—!!