Volume 2

"The Key to His Power" (強さの秘訣, Tsuyosa no Hiketsu) is the second volume of the One-Punch Man manga series.

Summary
A single man arose to face the evil threatening humankind.

His name was Saitama. He became a hero for fun. Three years of special training made him lose his hair, but he gained invincible power. He achieved such strength that he can defeat any opponent, however strong, with one punch. Unable to make use of his full strength, he is unsatisfied as a hero, but a cyborg named Genos asked to become his pupil! Then the House of Evolution takes an interest in Saitama's power and send monstrous assassins after him...

ONE
From now on, monsters of various design are sure to show up, so i'm excited!

Yusuke Murata
I first encountered the original One Punch Man on Twitter. I got to know the author there and then made a direct appeal to draw it. It was a very modern way to do things!