Turn Back The Pendulum 3

At the Second Division headquarters, Yoruichi waves Urahara through her grounds despite a protest from Suì-Fēng, and he hauls the uncooperative Hiyori inside by her collar. The chapter lays out how the Onmitsukidō, once separate from the Gotei 13, became bound to the Second Division once its commander also held a captaincy, with each of its five section heads holding a seat there. Urahara reveals that as Third Seat he led the Detention Unit, whose stated task was guarding criminals of the Seireitei. Pressed on his careful wording, he admits the unit also confined any Shinigami judged a potential danger, locking them in an underground facility called the Nest of Maggots.

Descending into the cavern, Urahara stresses that it is no prison: detainees cannot leave, yet move freely within, and have committed no actual crime beyond being deemed hazardous under Seireitei's rules. He explains the euphemisms that hide such transfers, where a prolonged leave of absence quietly becomes decommissioning, all sanctioned by the Central 46. Since taking command, he has believed these dangerous minds could become a great asset given the right setting. When a detainee suddenly lunges at Hiyori, Urahara notes the pit is a weapons-free zone and subdues the man barehanded, since every Detention Unit leader must. He then brings her to the single caged inmate, a shackled Mayuri Kurotsuchi, and offers him the chance to walk out.

The chapter exposes the Nest of Maggots and the quiet machinery by which Soul Society removes those it fears, disguising their vanishing as ordinary departures. It grounds Urahara's ambition to convert dangerous talent into power, the seed of the Research and Development Institute. Most significantly, it introduces Mayuri Kurotsuchi as the facility's lone caged detainee and sets up Urahara's offer to free him, the beginning of their long, uneasy partnership.

The third chapter of volume 36's Turn Back The Pendulum arc was adapted as part of Episode 208, Aizen and the Genius Boy. It supplies the origin of Mayuri Kurotsuchi's release from confinement and lays the groundwork for the Twelfth Division's research institute.