Saitama trained hard for three years straight! He lost his hair and became capable of killing his opponent with "One Punch!" However, his one shot powers had a cost. He became numb. No feelings at all. Until he met a particular cyborg, who just so happens to change everything...

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.