"Monsterization" (怪人化, Kaijin-ka) is the 72nd chapter of the One-Punch Man manga series.
It is revealed by the Super Fight Announcer that Gouketsu is the champion of the first Super Fight. Gouketsu then explains his disappearance that occurred several years ago. Orochi fought and defeated Gouketsu, but he spared Gouketsu's life in exchange for Gouketsu's service towards the Monster Association. Gouketsu accepted the deal because the Monster Association also offered him immense power with Monster Cells. After finishing his story, Gouketsu offers the martial artists a choice to either become monsters or die by his hand. Rosie rushes to eat one of the cells and then proceeds to attack an injured Dave. Choze snaps Rosie's neck and proceeds to eat one of the cells for himself. After transforming, Choze decides to knock Jakumen out of the ring. Benpatsu, Hamukichi, and Volten follow suit in eating the cells. Suiryu asks one of the civilians if he can go on a date with her if he beats up the monsters, which she nods to. With new motivation, Suiryu prepares to fight.
Suiryu approaches the martial artists who became monsters. He defeats Benpatsu, Hamukichi and Volten with ease, but is then confronted with the monster version of Choze, who proves to be a hard opponent even for him. Suiryu manages to provoke Choze, and the latter responds by launching a blast of energy from his horns, intending to kill everyone in the arena. Suiryu manages to send the blast away and fights Choze again. With Choze defeated, Suiryu confronts Gouketsu, who states it'd be a waste to simply kill Suiryu. He recognizes the man's strength and tells him he could become a high-ranked monster if he changed sides, and even guaranteed he'd be able to live an easy life. For a moment Suiryu seems to consider the offer, and nearly eats one of the monster cells, much to the other fighters surprise and grief. At the last moment, however, he states he has no intention to become an ugly monster like Gouketsu and attacks him. The chapter ends with Gouketsu striking a single hard blow on Suiryu, which seemingly injured him a lot.