Lab Arc

Running across roughly sixteen chapters, this arc pushes past the lighter opening of the series into territory that reveals Shin's origins for the first time. A cell answering to Kashima, one of the operatives inside the antagonist collective led by the man called X, seizes a hostage from the Sakamoto Store and hauls the victim off to a research site buried beneath a museum. What begins as a straightforward retrieval unfolds into a floor by floor descent, introducing the elite assassins of the Order and giving readers their earliest look at the story's central villain.

The opening beats stay comic. Sakamoto brings Shin to a department store to buy Hana a limited backpack for her first day of school, and a bounty hunter named Heisuke arrives with his bird Piisuke, only to be misdirected away from the store. The pair later cross paths with Heisuke at a neighborhood airsoft contest, where they team up and eventually beat him in a scuffle, turning a rival into a friend once he learns the photo he had been hunting from was just an old snapshot.

The mood shifts when a squad in full hazmat gear storms the shop while Sakamoto is out escorting Hana to school. Lu, wearing an apron marked with Shin's name tag, is grabbed in his place, and the intruders only realize their error after she overhears them insult Shin and lashes out. Returning to signs of a struggle, Shin explains his buried history to Sakamoto, who reveals tracking chips sewn into the name tags. Their pursuit leads to the Okutabi Science Museum, which sits atop a hidden laboratory. Heisuke, using Piisuke to follow the trail, brings a worried Hana along behind them.

Inside, Sakamoto and Shin battle animatronic museum displays before dropping underground, where captured researchers explain that Kashima's people had overrun the facility days earlier and stationed a boss on each sublevel from B1 through B5. Below them, Lu is locked up alongside Asakura, the lab's chief and the scientist who once granted Shin his clairvoyance. Elsewhere, the Order operatives Shishiba and Osaragi arrive chasing their own lead, and Osaragi swiftly cuts down two of Kashima's floor guardians. Kashima himself proves to be heavily augmented, hiding blades in his forearm, a laser barrel in his mouth, and an artificial spine. Just as he recovers from Shishiba's counterattack, Sakamoto crashes through the ceiling and lands squarely on him.

The lower floors erupt into parallel duels. Shin, aided by Heisuke, exposes and defeats the invisible assassin Seba by coating him in blood and water. Sakamoto, worn down into his lean fighting form, chases Kashima onto a passenger train in the underground shipping corridor, shields the civilians used against him, and finally puts the augmented killer down. As the facility collapses, Shin uses his clairvoyance to locate and evacuate the trapped staff. During the escape he senses two distinct voices yet sees only one figure, X, who steps past and calmly asks Shin to pass his regards to Sakamoto before vanishing.

The arc plants several threads that shape the rest of the series. Shishiba and Osaragi enter the story as agents of the Order, and X makes a chilling first appearance while quietly wiping out the Dondenkai agency. Heisuke and Piisuke join the cast for good, and Seba and Kashima are established as members of the villain group. Most importantly, Shin's past as a lab subject is laid bare, and his brief brush with X, sensing two personalities inside a single man, foreshadows the enemy's fractured identity that later becomes central to the plot.