Alien Conquerors Arc

Positioned as the eighth installment of the series and the fifth chapter of the Hero Association Saga, this arc also serves as the finale of the anime's opening season. It moves the story from a quiet dojo visit into full-scale interstellar warfare, tying the late prophet Shibabawa's grim warning to the arrival of an invading fleet from beyond the planet.

Bang offers to teach Saitama and Genos his signature Water Stream Rock Smashing Fist, but the pair turn him down, and his brash pupil Charanko loses a quick bout with Genos. The old master admits his once-crowded school was emptied when his finest student, Garou, crippled the other disciples before being cast out. An urgent Hero Association bulletin then pulls the S-Class ranks together, where Sitch breaks the news that the seer Shibabawa has died after choking on a cough drop, leaving behind a single dire note: the Earth faces catastrophe within six months.

The warning proves immediate. Skyfolk assault the headquarters, only to be wiped out by a colossal craft that reduces A-City to rubble in moments. The alien Melzargard, able to divide into several bodies, cuts down heroes until a team of four, Bang, Metal Bat, Puri-Puri Prisoner, and Atomic Samurai, corners him and destroys his hidden cores. High above, Tatsumaki hurls the ship's own missiles back at it. Saitama, meanwhile, punches his way aboard, flattening Groribas and Geryuganshoop before reaching the vessel's ruler.

Boros, who crossed the galaxy chasing a prophecy of a worthy rival, sheds his restraining armor and unleashes his Meteoric Burst, booting Saitama all the way to the moon. The hero leaps back in an instant, and after a furious exchange he answers the alien's ultimate Collapsing Star Roaring Cannon with a single Serious Punch. Dying, Boros realizes his opponent never once fought at full strength.

The alien warship plummets to earth, leaving A-City in permanent ruin. Sweet Mask executes the surviving invaders on the spot, while Metal Knight hauls off the wreckage to salvage its weaponry. The battle vaults Saitama into B-Class at rank 63, and the Association rebuilds its shattered base as a reinforced iron stronghold. Shibabawa's six-month deadline now hangs over every hero.