In One-Punch Man, Vol. 13: Monster Cells, the Class-A heroes are in a fierce battle against the giant monster Multieyed Octopus. As the situation intensifies, Class-S hero Flashy Flash enters the fray, adding his strength to the chaotic confrontation. Meanwhile, the Monster Association escalates its onslaught, but their ultimate objective remains shrouded in secrecy.

Amidst the action, the martial arts tournament advances to the semifinals, promising to showcase the prowess and skills of the remaining fighters.