Arc 10The Road to Hueco Mundo
Yan Si helped rebuild Soul Society, took on Tōshirō Hitsugaya as his disciple, and joined Kuroyashiki Kenpachi and Urahara Kisuke on an expedition to confront Aizen. The expedition reached Hueco Mundo, where Kuroyashiki battled Nnoitra and Starrk while Yan Si met Aizen at Las Noches.
- Yan Si defeated the Visored under his control, then helped them learn that Aizen had manipulated Seireitei and led them toward the hilltop confrontation.
- Aizen defeated the assembled Shinigami and Visored with Kyōka Suigetsu, then escaped to Hueco Mundo with Kaname Tōsen as Yamamoto and the others began reorganizing Soul Society.
- Yan Si was appointed captain of the Ninth Division and proposed a Court Security Guard Squad, while Gin Ichimaru and Kurotsuchi Mayuri received consideration for captaincies.
- Yan Si gave Mayuri a Soul Jade to awaken Kurayashiki Kenpachi, investigated how Shinigami could become human, and began a relationship with Yoruichi.
- Yan Si recruited Tōshirō Hitsugaya as his disciple and gave him Hyorinmaru, while Aizen transformed Nelliel into the third Espada and she established a peaceful palace for Hollows.
- Yamamoto sent Yan Si, Kurayashiki Kenpachi, and Urahara Kisuke to Hueco Mundo to investigate Aizen, and Yan Si left Enrakyōten for Tōshirō.
- At Las Noches, Kurayashiki fought Nnoitra and then Starrk, while Yan Si met Nelliel and sat down with Aizen as Tōsen went to confront Urahara.
- Yan Si told Aizen that the bones of Squad Zero formed the Ōken, and Aizen discussed how the Espada’s extreme emotions related to their power and evolution.