Marugori is a human that drank a steroid that turned him into a giant monster. After this he goes on a murderous rampage.
Marugori is first seen in the lab of his scientist older brother, Fukegao. He is handed a steroid called the Biceps Brachii King, It was strawberry flavored for easier ingestion. It turned him a Mysterious Being and was dubbed Beefcake. As Marugori heads to B-City his brother notices someone is sitting on the shoulder opposite to the one he is sitting. His brother yells, telling Marugori to kill him. Marugori swats at the wrong shoulder and kills Fukegao by accident. In his ensuing rage Marugori grabs Saitama and throws him to the ground. Saitama starts to get up, but Marugori jumps onto him and starts to punch Saitama repeatedly, leaving a giant hole in the ground. Believing himself victorious, Marugori begins to mourn for his brother until Saitama jumps out of the hole and punches him in the face, killing him and sending him crashing onto B-City, destroying it.
- Marugori is the first Mysterious Being in the series to receive a disaster level threat.
- Marugori shares some similarities with Eren Yeager of Attack On Titan as both transformed into giants and coincidentally share the English voice actor Bryce Papenbrook and Latin American Spanish voice actor Miguel Angel Leal.