Saitama vs. Pluton

Saitama vs. Pluton was the battle between the B-Class hero Saitama and the mysterious being Pluton, King of the Underworld.

Prelude
Pluton is first seen in Z-City, but has now appeared in Y-City. The King of the Underworld states that humans waste their existence in decadence and gluttony, littering the planet with worthless objects. As he continues to wreak destruction, Pluton proclaims that they shall rot in the underworld that spreads below his snout. He is about to kill an innocent child, but Genos saves the child right before the building collapses over him. Pluton notices Genos and asks who the cyborg is. Genos states that there is a great man who is a hero for fun and profit. Pluton lifts his head when he notices something headed toward him.

Battle
Saitama jumps towards the Dragon-level monster's head, blowing it apart with a single punch, making Saitama the victor. Upon killing Pluton, Genos smiles and continues his statement by saying he is Saitama's disciple, surprising the child he saved. Dozens upon dozens of gallons of blood spread across the city, as well as Pluton's intestines. Saitama looks at his steaming glove, frowning that he defeated Pluton with a single punch, and yells out "Damn it!" to the sky.

Trivia

 * This is the final battle in season 1 of the anime.
 * It is also an anime-only fight.