Chapter 172: I.o.

As the rival fists close the final gap, Blast tears open a gateway and drags all three of them past the planet's edge. Once in the void the punches finally meet, and the resulting shockwave threatens everything below. Backed by allies from other dimensions, Blast bends the destructive wave away from Earth and keeps it whole. The rebound, however, hurls Saitama and Garou far across the solar system until they slam down onto Io.

Recovering on the Jovian moon, Garou proposes finding a route home, but Saitama cuts him off, declaring that beating the Hero Hunter comes first. Saitama briefly weighs slotting Genos' core into his suit, then keeps it in reserve. Garou tries to fight with portals, opening one under Saitama and another at his back, yet Saitama simply kicks the first aside, seizes the edge of the second, and flips it to land another blow. Mocking the trickery, he demands Garou fight with his fists.

Garou answers with a barrage, chaining Roaring Aura Sky Ripping Fist, Water Stream Rock Smashing Fist, Exploding Heart Release Fist, and Whirlwind Iron Cutting Fist before finishing with Nuclear Fission Gravity Knuckle, an explosion that rips Io apart. Saitama's suit is wrecked but his body stays untouched. He counters with Serious Table Flip, prying up the crust and burying Garou in flying rock, then hunts him through the debris with Omnidirectional Serious Punch, striking from every side at once. When Garou flees into a portal, Saitama follows and knocks him back out. Cornered at last, Garou triggers Mode: Saitama, and the two crack each other across the face at the same instant.

Listed as the one hundred seventy-second installment, this chapter runs under the Monster Association Arc and appears in Volume 34, with Viz publishing it as Io. Saitama and Garou share the cover, and the events adapt webcomic chapters 89 and 90. A volume bonus illustration shows Saitama frozen in a post-strike stance, Genos' core cradled in his free hand.