A cyborg named Genos tracks down a mutant called Mosquito Girl, whose mosquito swarm drains the blood out of everyone they come across within the city. Genos has a difficult time with Mosquito Girl who almost forces him to activate his self-destruct as a last resort to stop her. Saitama then suddenly stumbles into the fight, easily killing Mosquito Girl. Despite Genos's extremely boring explanation of his past, Saitama agrees to make Genos his apprentice. Soon after, Mosquito Girl's fellow mutants from the House of Evolution try to capture Saitama, with only Armored Gorilla surviving as he agrees to answer the heroes' questions.