Kiri, a summoned hero, has acquired amazing strength as a result of 300 years of training out of caution. In order to return to his original world, he has taken Eimu, a naive girl who is the daughter of the "Demon King," as his apprentice to train her to become the most powerful along with the addition of May to train, a beautiful sword princess who has her very own problems, Kiri begins a journey where they will do whatever they want, no matter what kind of monsters they face in their path