The Strongest Hero

The battle with Boros escalates until the alien loses an arm, and the exchange eventually flings Saitama to the Moon before he leaps back. Elsewhere, Mumen Rider, Stinger, and Lightning Max pull the last survivors clear, while the S-Class heroes finish Melzargard when a recovered Bang shatters the final marble in his last head. Boros reveals his own regeneration, forcing both combatants to unleash their strongest attacks, but Saitama prevails and Boros concedes he never came close. Afterward, Drive Knight departs, warning Genos that Metal Knight is his enemy, and Sweet Mask arrives to blame the S-Class for the city's ruin, nearly sparking a brawl until Metal Knight surfaces to salvage the wreckage.

Superalloy Darkshine uncovers surviving aliens, whom Sweet Mask swiftly eliminates as Genos sees a reflection of his own past in him. Emerging from the ship, Saitama finds Tatsumaki throwing a tantrum; Genos snaps at her and is promptly slammed into a rock before Bang defuses the situation. The parts Metal Knight recovers are used to rebuild the Hero Association headquarters on the site of A-City, which is erased from the map, and the top heroes are invited to stay there. In a scene after the credits, the Dragon-level being Pluton rampages through Z-City, only for Saitama to end it with one punch as he laments that life has returned to single-blow victories.

Saitama defeats Boros to close out the alien invasion, and Bang finishes Melzargard for good. Drive Knight warns Genos about Metal Knight, the Hero Association headquarters is rebuilt over the vanished A-City, and the post-credits arrival of Pluton reaffirms Saitama's frustration with effortless wins.

The rescue efforts of Stinger, Lightning Max, and Mumen Rider are anime-original, as is the entire Pluton sequence and Sweet Mask's conversation with Genos. This marks the first episode to skip its opening, with the theme playing during the Saitama and Boros fight instead, and the only one to run its ending theme over the episode itself.