JCC Infiltration Arc

This is the fifth story arc of the Sakamoto Days series, spanning chapters 73 through 104 across volumes 9 to 12, with its anime adaptation beginning at episode 22. Following their entrance into the JCC, Sakamoto and Shin operate undercover to reach the academy's secret database, unaware that Slur is chasing the same prize from the shadows.

When Sakamoto's active bounty disqualifies him from enrolling despite his passing marks, Nagumo suggests he sneak into the JCC as a teacher wearing his wife Aoi's face, while the top-scoring Shin joins as a student. The two comb the academy for its fabled database, crossing paths with the eccentric weapons designer Natsuki Seba, whose signal-blocking hood foils Shin's mind reading and who turns out to be Mafuyu's brother. Elsewhere, the newcomer Amane clashes with Sakamoto using a four-section staff, and Sakamoto recognizes the technique of the exiled assassin Yotsumura.

Shin learns that the so-called database is not a machine but a person, the veteran janitor Byodo, and that senior instructor Satoda holds the key to finding him. Meanwhile Slur's people close in, having steered Amane through hypnosis and manipulation into striking at the academy's defenses. Once Amane knocks out the security system, Kanaguri and Club Jam lead an assault, with Club Jam's mass hypnosis turning the student body into a weapon.

The invasion turns deadly as Kanaguri cuts down Satoda and tells a grieving Akira that Slur was the one who killed her aunt Rion. Sakamoto sheds his disguise and reclaims his lean fighting form to battle Kanaguri, while Shin, Natsuki, and a freed Amane overwhelm Club Jam. Away from the school, Shishiba hunts down Yotsumura, and their duel unspools the tragedy of how Yotsumura's assassin wife Shino betrayed him and how he was framed for a killing he did not commit.

The arc introduces a dense web of new players. Club Jam, Amane, Byodo, Satoda, and the tragic Yotsumura all debut, and their ties run deep: Yotsumura is unveiled as a former Order member and Shishiba's mentor, Amane as his son, and Byodo as both the living database and Amane's grandfather. Shishiba defeats Yotsumura and casts him into a river, only for Nagumo to fish him out and press the fallen assassin into service. Shin also comes away with a delayed-activation glove built by Natsuki.

By the end, the academy shutters for days to bury its dead and repair the damage, and many students abandon their worship of X. Byodo shares that the mastermind's real name is Uzuki and floats the theory of a split personality, a suspicion that reframes Shin's earlier encounter with him. Kanaguri is expelled from the Order, Akira departs alongside him vowing to avenge Rion by killing Slur herself, and Uzuki's organization regroups to press on with its war against the Order, leading into Taro Sakamoto's Past Arc.