Saitama is a hero who only became a hero for fun. After three years of “special” training, though, he’s become so strong that he’s practically invincible. In fact, he’s too strong—even his mightiest opponents are taken out with a single punch, and it turns out that being devastatingly powerful is actually kind of a bore. With his passion for being a hero lost along with his hair, yet still faced with new enemies every day, how much longer can he keep it going?
This tv show contains 24 potentially triggering events.
The villain Super S is basically a dominatrix. She whips people and attempts to turn them into her "love slaves." She also wears a tiny, tight harness and tall boots and not much else.
A hero named Puri Puri Prisoner gets absolutely destroyed by the sea king in the middle of season 1 after being very vocally gay. He talks about his boyfriend making him a sweater and calls all of the men he interacted with his boys, a few minutes after he's introduced he's punched with intent to kill several times. They say all of the heroes are in critical, he survives fine and goes to see two of the boys after but he's still treated very much like a joke when he shows up.
Puri-Puri Prisoner rips off all his clothes when he powers up. Saitama's clothes are burned off at one point. Actual genitals are hidden by posing or shadows.
Throughout the show, the protagonist contemplates his unenjoyment in life, and how his weaker opponents fail to thrill him. This feeling is shared with his opponent in the season 1 finale. In S2E9, he and a supporting character have a textbook nihilism vs. existentialism conversation.