One-Punch Man, Vol. 21 by ONE

[Viz] Life gets pretty boring when you can beat the snot out of any villain with just one punch. Nothing about Saitama passes the eyeball test when it comes to superheroes, from his lifeless expression to his bald head to his unimpressive physique. However, this average-looking guy has a not-so-average problem—he just can’t seem to find an opponent strong enough to take on! The curtain rises on the big battle between the Monster Association and heroes! As the lower-ranked heroes engage in intense battle, the Class-S crew takes out many monsters in one fell swoop before venturing further underground. Among them, Flashy Flash demonstrates splendid battle prowess against a duo of monstrous ninja!