Chapter 23: Threat from the Sea

A hulking creature climbs out of the ocean to menace a coastal city, naming itself among the Seafolk and ordering humanity to hand over dry land. Saitama ends its tirade in an instant. A second wave then floods the shore with more Seafolk, and when they overrun J-City the A-Class hero Stinger steps up alone, only for the Deep Sea King to fell him the moment he thinks he has won.

The first Seafolk to surface rampages briefly before Saitama shows up and drops it without effort. Soon a towering wave delivers a fresh pack of the invaders, who storm into the streets and seize a civilian, until Stinger snatches the victim to safety and calls out the rest. The story then cuts to Saitama and Genos unwinding at home, where Genos, washing dishes, muses on their climbing ranks and figures Saitama may soon reach B-Class, noting that the current top-ranked C-Class hero has held the spot for over half a year. A call from the Hero Association reports the Seafolk assault on J-City, and once Saitama flips on the news and sees a bloodied Stinger still standing his ground, he turns serious and insists they hurry.

Cornered by several massive Seafolk, Stinger is told his allies have fled and that death awaits him, but he shrugs off the taunts, deciding that being on his own means he can cut loose. He counters an incoming strike with one of his own that punches clean through a Seafolk, then vaults through the gap and finishes the last three. His celebration lasts only a breath before the Deep Sea King strikes him down. In a bonus page, D-Pad barrels toward J-City in his truck with Funeral Suspenders, Studless, Skunk Boy Gasmask, Hyottoko, Food Battler Futotsu, and a pack of other C-Class heroes, only to be blown past by Saitama and Genos.

"Threat from the Sea" (Umi Kara no Kyōi) is the twenty-third chapter of the manga and opens the Sea Monster Arc. Split across two parts, it went out on April 19, 2013 and May 2, 2013, running twenty-seven pages online and twenty-six in Volume 4. It draws on webcomic chapter 24, corresponds to Tonari numbers 28 and 29, and was adapted as Episode 8 of the anime. The chapter follows "Voices" and precedes "Deep Sea King."