"Deep Sea King" (深海王, Shinkaiō) is the 24th chapter of the One-Punch Man manga series.
The chapter begins with a city alarm announcing that the disaster level of the Seafolk invasion has been raised to Demon. In addition, the citizens are advised to evacuate the city. The Deep Sea King continues to walk through the city. Lightning Max is seen observing the Sea King from afar. The Deep Sea King then suddenly appears behind Lightning Max and their fight initiates. During the fight is overwhelmingly one-sided and Lightning Max ends up losing. Puri-puri Prisoner comes in time to save Lightning Max from being crushed by a building. It is revealed that Speed-o'-Sound Sonic has followed Puri-puri Prisoner and Sonic thanks him for allowing him to escape. Puri-puri Prisoner becomes excited to fight the Deep Sea King after sensing the King's strong aura. The two then begin fighting while Sonic observes. Puri-puri Prisoner ends up taking a lot of damage and resorts to using his Angel ☆ Style transformation. However, it is proven to be useless as the Sea King was still able to beat Puri-puri Prisoner. After Sonic and the Deep Sea King have a small chat, they begin fighting. During their fight, it starts to rain. Sonic's speed seems to be too much for the Deep Sea King.
Sonic's fight with the Deep Sea King continues, but the Sea King gets a noticeable speed, strength, and size boost. Sweet Mask is briefly seen on television, he tells the interviewer a little about his ideology about what a hero is in his mind. The Deep Sea King is later seen chasing Sonic and is able to grab him. However Sonic was able to slip through, leaving his clothes behind. Sonic then tells the Deep Sea King that the next time they meet, it will be the Sea King's last. Sonic bumps into Genos while on his way to get his weapons. Before Sonic leaves, he tries to belittle Genos' hero career. Afterwards, the Deep Sea King decides to go to one of the shelters. He was able to effortlessly make a hole in one of the walls of the shelter. Before he could attack the people C-Class hero, All Back-Man, interrupted him. The B-Class hero, Jet Nice Guy, the C-Class hero Bunbunman, and A-Class hero, Sneck, followed All Back-Man's lead soon afterward. The chapter ends with the crowd cheering for the heroes as the heroes prepare for battle.
- In the Volume release, the chapter was split into two parts, with part one being published in Volume 4 and part 2 being published in Volume 5.