Saitama and Genos find out about the hero registration and both take the tests to certify. Genos gets "S(Special)" and Saitama gets a "C" grade. Meanwhile, Genos became the disciple of Saitama and learned about the power of saitama's punch on a training session.

An enormous meteor hurtles toward City Z, forcing the Hero Association to ask its S Class heroes to respond. When all their efforts prove in vain, Genos decides it's up to him to protect the home of his master and stop the meteor, no matter what the cost.