Byakuya
Kuchiki

Byakuya Kuchiki is the 28th head of the Kuchiki clan, captain of the 6th Division, and the man who stands calmly by while his own adopted sister is sentenced to death. His logic is airtight and monstrous: he broke the rules twice in his life, once marrying a commoner, Hisana, and once adopting her little sister Rukia as a deathbed promise, so he swore he would never break another. If the law says Rukia dies, Rukia dies.

Ichigo exists to break exactly this kind of man. Their Bankai-against-Bankai duel at Sokyoku Hill, Senbonzakura Kageyoshi's million blade petals against Tensa Zangetsu, ends with Byakuya cut down and quietly admitting that Ichigo was right to fight for her. From then on the ice thaws by degrees. He kills the seventh Espada to protect Rukia in Hueco Mundo and answers her surprise by saying he came because she is his pride.

The Thousand-Year Blood War nearly kills him in its first week. As Nodt turns Senbonzakura's own petals against him and leaves him broken in the rubble, begging Ichigo, of all people, to protect Soul Society. He survives, retrains in the Royal Palace, and comes back measured and terrifying, apologizing to his squad for showing them something so unsightly. By Part 3 he is one of the spearheads of the Wahrwelt invasion, standing beside Shinji and Urahara when Gerard Valkyrie lands in their path.