Chapter 3

"A Dangerous Being" (災害存在, Saigai Sonzai, Tonari: 3) is the third chapter of the One-Punch Man manga series.

Summary
The chapter opens on Fukegao, who has just finished his new, ultimate steroid, Biceps Brachii King. Fukegao gives his new steroid to his little brother, Marugori, claiming that it will make him the strongest man alive. Marugori drinks the drug and his body immediately starts to transform, growing till he crashes through the ceiling and becomes taller than the surrounding hills. Marugori picks his brother out of the rubble of the building and sets him on his shoulder, who then proclaims them The Brain and Brawn Brothers, the strongest, most intelligent group in the world. The two of them head to the nearest civilization, D-City, the entirety of which he destroys in one swing of his arm, Fukegao then says to go on and destroy the next city.

The country is in an uproar and multiple news stations report the disaster. As they head to the next town, B-City, Fukegao notices that there is someone sitting on Marugori's other shoulder, that someone being Saitama. Marugori mistakes which shoulder Saitama is on and accidentally swats the wrong shoulder where his brother is on, killing him instantly. When Marugori finds out whom he has killed, it was not Saitama whom he has killed but was his older brother Fukegao. After this, He then freaks out, lamenting that all he'd wanted was to have more power, and blames his brother's death on Saitama, grabbing him off of his shoulder and throwing him to the ground with all his anger. Saitama begins to get up and brush himself off when Marugori jumps on top of him and starts pounding Saitama back to the ground, leaving a gigantic hole. Thinking he victoriously defeated him, Marugori recalls feeling empty inside despite being the strongest, with Saitama agreeing, jumps out of the giant hole and then punches Marugori in the face, killing him, landing Marugori on to the B-City, accidentally destroying it.