A video game lover withdrawn from society, Satou Kazuma's life should have ended suddenly in a traffic accident. However, he is later reincarnated into a parallel world dragging a goddess, Aqua. Afterward, in a fantasy world with RPG-like aspects, Kazuma aims to enjoy an "Adventurer's" life and to become a Game Hero. However, before long, his happiness fades away with the continuous troubles made by his party members. They are a troublemaking goddess, Aqua, an Arch Wizard with serious "eighth-grader syndrome," Megumin, and a masochist with fantasy, Darkness.These three with most annoying personality traits always get Kazuma into trouble. Therefore, he is sometimes heavily in debt, once suspected of the crime of subversion to the state, sometimes battles the Devil King's generals, and even dies…One day, Yunyun, who is also a Crimson Demon girl, occurs all of a sudden. She says shockingly she wants to have Kazuma's children. They find that the Crimson Demon village is facing an unprecedented threat. Yunyun later goes back to save their hometown; soon Kazuma and others also head for Crimson Demon village afterward. However, they will face the biggest crisis! What will become of Kazuma's life in another world?