Episode 22

Saitama keeps losing to King at a fighting game and, on a break, spots King's Emergency Transmitter. Elsewhere, Gyoro Gyoro and Destrochloridium hijack a Hero Association executive to propose coexistence between monsters and humans, then Destrochloridium murders an executive and drops the pretense, revealing the real aim, to lure every hero into one all-out battle against the Monster Association. When it turns its pistols on the surviving executives, Superalloy Darkshine intervenes and kills it after its mind control fails to take hold. Gyoro Gyoro and Orochi rally the monsters for the coming war, and Orochi devours Awakened Cockroach for his defeat while sparing Do-S for her useful powers, only to learn from Gyoro Gyoro that Gouketsu is dead.

Word of the impending war spreads to the public and to unaffiliated monsters, and when the rogues gather hoping to enlist, Saitama, running late for garbage duty, wipes them all out. Garou wakes from Saitama's kick, spots the A-Class hero Death Gatling, and, too worn out to fight, retreats to a shack to rest, though Death Gatling clocks his position. The boy Tareo, pushed by his friends, is sent to evict the intruder, and their reunion prompts Garou to tell him that if he does not want to be pushed around, he should grow stronger. Genos receives fresh upgrades from Dr. Kuseno. Death Gatling closes in with his team, Stinger, Smile Man, Wildhorn, Chain'n'toad, Glasses, Gun Gun, and Shooter, and Garou, after a glance at Tareo's hero almanac, throws himself at them boasting that beating them will make a hundred heroes felled. The barrage keeps him off balance, and when he singles out Glasses as the likely weak link he finds the man just as willing to fight, leaving the heroes to offer the fading hunter one final chance to give up.

The Monster Association exposes its true plan for a single decisive war and Superalloy Darkshine kills Destrochloridium. Orochi confirms Gouketsu's death after eating Awakened Cockroach. Saitama annihilates the rogue monsters seeking to join the Association. Garou grows closer to Tareo and receives a hero's advice in reverse, then is surrounded and worn down by Death Gatling's coordinated squad.

Titled Justice Under Siege, this Monster Association Arc episode adapts chapters 79 through 81. It aired in Japan on June 18, 2019, and in English on December 14, 2019, with Seijaku no Apostle and Chizu ga Nakute mo Modoru Kara as its themes. In the adaptation, the heroes hunting Garou are not given the additional descriptions of their abilities that the manga provides.