Ever since Saitama accepted Genos as his disciple, they spent a lot of time together. Now, as an A-Class Hero, Saitama is finally allowed to fight evil side-to-side with Genos. However, the relationship between him and his disciple isn't only a pure teacher-student-relationship.
villain!Saitama travels back in time to his younger self, and sends him and Genos to their past, which leads to some unexpected surprises. Genos is still human, and Saitama still has hair, but he is not he strongest man in the world anymore. Their mission? To stop the Hero's Association from making one simple thing: Z...