Aizen and the Genius Boy

Newly appointed captain Kisuke Urahara escorts Hiyori Sarugaki onto Second Division grounds, waved through by Yoruichi Shihōin over Suì-Fēng's objection. He explains how the Onmitsukidō merged with the Gotei 13 under Yoruichi and describes the Detention Unit, a hidden facility for Shinigami deemed too dangerous or troublesome to leave free. The pair descends into the cavern-like Nest of Maggots, where Urahara notes the inmates may act as they please but can never depart.

Inside, a former classmate of Hiyori's nicknamed Big Mouth begs for help, and when the prisoners attack, Urahara subdues them barehanded, since weapons are forbidden there. He then leads Hiyori to the single inmate confined to a cell, Mayuri Kurotsuchi. Urahara offers Mayuri the second seat of a new organization he plans to found, the Shinigami Research and Development Institute, promising the institute will one day be his. Mayuri accepts.

At the Kuchiki estate, a young Byakuya trains under his grandfather Ginrei until Yoruichi appears, taunting him, snatching his hair tie, and vanishing with Shunpo as he gives chase. In the Thirteenth Division, Kaien Shiba again declines Ukitake's offer of the lieutenant post while Ukitake mentions a prodigy who graduated the Academy in a single year. That night, Lieutenant Aizen praises a boy standing over a slain Third Seat, learning his name is Gin Ichimaru. Nine years later, three shadowy figures watch as several Souls suffocate and die.

Urahara reveals the workings of the Nest of Maggots to Hiyori. He recruits Mayuri Kurotsuchi to co-found the Shinigami Research and Development Institute. Yoruichi torments a young Byakuya at the Kuchiki Manor. Ukitake hints at a rising prodigy in the Fifth Division. Aizen takes an interest in a young Gin Ichimaru after Gin kills a superior officer.

Set within the Turn Back the Pendulum arc, this episode adapts material from Chapters -106, -105, and the opening pages of -104. The opening theme is Velonica and the ending is Sky Chord ~Otona ni Naru Kimi e~. It aired in Japan on February 24, 2009, and in English on June 11, 2011. No formal battles occur across the episode. Its closing omake, the Substitute Shinigami Work Diary, has Ichigo and Rukia failing to recall Zennosuke Kurumadani's name.