Chapter 15

Nagumo greets Sakamoto and claims to have caught him in the act, then tells Shin he has wiped out the Dondenkai leadership, boss included, and that Sakamoto must die as well. Moving in a blur, he slips behind Shin and drives a knife into his throat, only to laugh it off and reveal a prop blade that fooled everyone but Sakamoto.

Pressed on why he is there, Nagumo says his business with Dondenkai was already moot since the whole group lay dead when he arrived. He explains he is investigating a string of massacres in which countless assassins have been slaughtered by an unknown culprit. When Shin shrugs at killers dying, Nagumo lays out the scale: some thirty outfits tied to the JAA have been struck and over a thousand professionals murdered within a few months, a deliberate signal aimed squarely at the association. Shin is stunned that the toll amounts to a quarter of the whole trade.

The killer signs each scene with an X, earning the name X, also called Slur. Sakamoto wonders aloud whether the Order has picked up the case, and Lu, having overheard Tatsu mention it, wonders who they are. Nagumo describes the Order as the association's elite enforcement squad, tasked with restoring balance whenever conflict in the assassin world grows dangerous, and adds that Sakamoto once served among them. Lu is floored and Shin cannot believe he never knew. Nagumo cautions Sakamoto to be wary of X, but Shin protests that former assassins have no reason to worry about a killer of killers, and Lu notes the bounty on Sakamoto is already consuming their attention. Nagumo points out the murders began right around when that bounty was posted.

Elsewhere a mysterious man reads a beginner's drawing book amid a floor strewn with corpses, then marks an X on the wall. Back at the Sakamoto shop, Shin groans that they are no closer to answers when yet another assassin attacks. Lu helps Hana trigger a register mechanism that dumps a pile of guns onto the intruder, and Aoi finds small comfort in booming bandage sales. Recalling Nagumo's warning that his skills have dulled during the hiatus, Sakamoto decides that if the enemy is unknown, the only sound answer is to grow strong enough for anything. He trains by ferrying Hana to school on a bicycle, Shin sharpens his mind-reading by serving customers, and Lu, remembering that she fights better drunk, opts to train herself by drinking and clocks a customer who turns out to be an assassin.

Nagumo reveals he wiped out the Dondenkai and startles the group with a fake-knife prank. He explains that an unknown killer has slaughtered over a thousand assassins across roughly thirty JAA-linked groups, a figure marking each scene with an X and known as Slur. Nagumo discloses that Sakamoto once belonged to the Order himself and warns him to watch for X. The mysterious killer is shown drawing an X at a crime scene, marking his debut. Sakamoto resolves to train the family, having noticed his abilities have slipped during his years off.

This chapter, part of the Amusement Park Arc and Volume 2, bears the Japanese title Shido, meaning Initiation. It debuts Kei Uzuki as the shadowy killer X, also called Slur, and delivers key backstory by revealing Sakamoto's past as an Order member and the scale of the assassin massacres tied to his bounty.