Complex sentence: Saitō and the other applicants of the Rōshigumi who remained in Kyoto become retainers to the Aizu clan and the Rōshigumi is renamed the "Mibu Rōshigumi".
Split into simpler sentences: Saitō and the other applicants of the Rōshigumi who remained in Kyoto become subordinates in the Aizu clan. The Rōshigumi is renamed the "Mibu Rōshigumi".