One Punch Man

A monster named Vaccine Man wreaks havoc in a city before he is easily killed by a bald superhero named Saitama when he was about to kill a young girl. Since saving a boy with a cleft-chin from Crablante three years ago, Saitama aspired to become a hero but became too powerful as he easily defeats enemies with a single punch. Following taking out the The Brain and Brawn Brothers, one of whom was a huge giant, Saitama has a dream about a subterranean race who invade and actually pose a challenge to him, something he has been missing for years. But when Saitama wakes up, he finds that the subterraneans are extremely weak and easily killed by him as he one-shots their leader and the rest immediately retreat.