Chapter 18

A slip by Lu tips Heisuke off to Sakamoto's real identity, and the sniper immediately switches sides, reasoning that betraying the pair nets him both the airsoft prize and the assassin bounty. After Sakamoto's group fends off a rival team, Piisuke delivers a rifle case so Heisuke can assemble his weapon. He trains his sights on Sakamoto's forehead and fires mid-leap; Sakamoto cannot fully evade and takes the round through his hand. Shin moves to give chase, but Sakamoto reins him in so they keep playing the tournament.

Alone and in tears, Heisuke insists he feels no grief, telling himself the two are simply enemies and that this is his moment to earn recognition as a real killer. As the match nears its finish, Shin fails to pinpoint him, while Piisuke quietly feeds the sniper their position. A ricochet nearly catches Sakamoto, who notes that the bullet spun oddly, as though built to bounce. Heisuke confirms they are triple rebound rounds, engineered so their trajectory stays unpredictable.

When Shin demands to know what became of their friendship, Heisuke answers coldly that assassins see only targets through a scope. A flashback lays out his past: hopeless at nearly everything but shooting, he cleared the assassin academy and joined an agency, only to be scorned by a superior and cast out once his colleagues judged him worthless. Chasing Sakamoto's bounty became his bid to matter. Shin cuts through the self-pity, telling him that other people's opinions mean nothing beside self-belief.

Shin's outburst rattles Heisuke enough for Shin to read his mind and steer Sakamoto to the hiding spot. A thrown rock wrecks the rifle, and Heisuke goes down, handing the tournament win to Sakamoto and Shin. Still weeping that he has failed even at his one gift, Heisuke says they cannot grasp what weakness feels like. Sakamoto rejects that, praising him as an extraordinary marksman, and the grateful sniper collects his cut of the winnings: fifty yen.

Heisuke Mashimo betrays Sakamoto and Shin after learning that Sakamoto is the legendary hitman, chasing both the prize and the bounty. He debuts his triple rebound bullets, rounds designed to ricochet along paths that are hard to predict, and wounds Sakamoto's hand. Piisuke secretly relays the team's location to aid him. Shin telepathically locates Heisuke, and Sakamoto smashes the rifle with a rock to end the fight. Sakamoto and Shin claim the airsoft tournament, and Heisuke walks away with fifty yen.

This chapter carries the Japanese title Bui Esu Sunaipā and sits within the Lab Arc, collected in Volume 3. It was published in issue 18 of 2021 on April 5, 2021, and runs twenty-one pages. The installment delivers Heisuke's full backstory, framing his loneliness and self-doubt, and marks his shift from antagonist toward a member of Sakamoto's circle. Lu Shaotang and Piisuke also feature in the events.