Chapter 173 (Online): Secret Intel

Reviewing the collapse of his defense grid, Bofoi identifies the culprit as A-Class Rank 39, the Caped Baldy. Digging through the association's records, he sees a hero who has vaulted up the ranks through countless fights and now tops the physical-testing charts. Judging that Saitama likely outclasses even the S-Class, Metal Knight decides to keep him under surveillance.

Two days prior, a closed meeting gathers Genos, Flashy Flash, Sweet Mask, Zombieman, Sekingar, and Sitch. Sitch ties the Monster Association crisis to the prophecy of Earth in danger and demands secrecy. Zombieman recalls Homeless Emperor invoking God with his dying breath, and Flashy Flash reveals he too once met a telepathic presence offering power. Sitch discloses that for two decades Blast and his companions hunted a mysterious cube that communicates with God, and that during a clash with Elder Centipede two years earlier, Blast met the entity face to face, refused its power, and fought it alone.

Genos insists Saitama could have resolved everything had the intel not been buried, then recounts the battle against Garou. Four exhausting hours later, with Sweet Mask having slipped out, the group dismisses the account as dubious and wants to verify it with Saitama, only for Genos to reveal that Saitama remembers none of it, prompting Flashy Flash to call him a liar and enrage the cyborg. Sitch concludes that unity among heroes is the priority to deny God any foothold in weak spirits. As Genos departs, Zombieman connects Dr. Genus' remark about a man trading his hair for a broken limiter to Saitama, while Flashy Flash and Sweet Mask both begin to suspect the Caped Baldy is far more than he appears.

The 173rd chapter falls within the Psychic Sisters Arc and is titled Hitoku Jōhō, rendered by Viz as Secret Info. It partly adapts webcomic chapter 97, and its cover features Genos, Sweet Mask, Flashy Flash, and Zombieman.