Sōsuke Aizen
Byakuya first appears on a mission with his lieutenant, Renji Abarai, to capture Rukia Kuchiki and kill Ichigo Kurosaki. They succeed in retrieving Rukia, and would have easily killed Ichigo, if not for Rukia's intervention, pleading for Byakuya not to give the finishing blow. Byakuya later interrupts Ganju Shiba and Hanatarō Yamada's attempt to rescue Rukia and, later on, Renji's attempt to do the same. Byakuya then fights Ichigo for the third time. Following Ichigo's inner hollow's forced submission, both focus their remaining power into one final attack, resulting in a tie. At the end of the battle, Byakuya, through their conversation, realizes that what Ichigo has fought against is the law of Soul Society instead of Byakuya himself, after which he gives his word not to capture Rukia again for her execution. Later, when Sōsuke Aizen orders Gin Ichimaru to kill Rukia, Byakuya intervenes and shields Rukia from Gin's attack. While being treated, Byakuya tells Rukia why she was adopted, apologizes to her, and thanks Ichigo. Afterwards, Byakuya's attitude toward Rukia changes significantly. He is seen to care for Rukia in an indirect manner and displays a new view on the idea that the law is never perfect.