The Lone Cyborg
A monster is moving toward City Z, one that has been created by the mysterious organization known as The House of Evolution. Genos, a young cyborg, attempts to stop it, but gets in over his head before Saitama happens along.
Aired 06/09/2015EP 2 - The Lone Cyborg
2015
One-Punch Man
Saitama has a rather peculiar hobby, being a superhero, but despite his heroic deeds and superhuman abilities, a shadow looms over his life. He's become much too powerful, to the point that every opponent ends up defeated with a single punch.
The lack of challenge has driven him into a state of apathy, as he watches his life pass by having lost all enthusiasm, at least until he's unwillingly thrust in the role of being a mentor to the young and revenge-driven Genos.