The Seafolk Tribe openly declare war on humanity. Saitama easily kills an octopus-like monster while on his way home. Mumen Rider is late to the scene and sees only the destroyed body of the creature, and hears the crowd talking about Saitama. Mumen looks Saitama up on the internet and finds that he is powerful, but opinions are divided on him. At the coast, several large Sea-Folk monsters emerge from the sea, threatening City J. The Class A hero Stinger (rank 11) challenges them with his powerful Bamboo Shoot weapon...