Many heroes and villains rise to prominence in the story of Bleach, and although Ichigo Kurosaki is a gruff and well-meaning protagonist, he might not even be the most compelling one. Captain Byakuya Kuchiki is a complex character who began the story as a villain of sorts but underwent a personal story arc that transformed him into a hero. When Byakuya's most heroic scenes and most villainous scenes are compared side by side, it quickly becomes clear how far this character has come.
The Overbearing Commander
Byakuya Kuchiki made a frightening first impression when he intervened in Ichigo and Renjki's stubborn duel. At the time, Rukia was being escorted back to the Soul Society for the crime of passing her powers to a human, and Byakuya had had enough. With a single flash step and quick sword strike, he very nearly killed Ichigo, leaving him to die as he dragged Rukia back through the Senkaimon gate. Ichigo wouldn't see Byakuya again for some time, but the viewers would.
Cold efficiency was Byakuya's game, similar to Ulquiorra Schiffer. Captain Kuchiki was the ruthless enemy of Ichigo, and worse yet, he had no compassion for his adopted little sister, Rukia. Byakuya had once broken the law by marrying a commoner, Hisana (Rukia's big sister), and he broke the law again by adopting Rukia into the family. At the time, Byakuya was convinced that following the law and maintaining order came before any personal interest, even at the cost of someone else's life. So, Byakuya upheld his little sister's cruel and unfair execution sentence, and he expected his Lieutenant, Renji Abarai, to feel the same way.
When Ichigo stormed the Soul Society with his friends, Ichigo turned Renji to his side, and that led Renji to come to blows with his ice-cold Captain. Byakuya badly injured Renji, who was taken to prison instead of the hospital. Around that time, Byakuya also came face-to-face with Ganju Shiba, the little brother of Kukaku Shiba, and struck him down when Ganju tried to get revenge for his fallen brother, Kaien Shiba.
The Brother's Heart
Byakuya's morality shifted in the face of Ichigo's defiant protection of Rukia. Once Sosuke Aizen was outed as the traitor who schemed to get Rukia executed, Byakuya re-assessed himself and his role as a Captain, as a nobleman and as a big brother. He made peace with Ichigo's group and Rukia, and he admitted that his blind obedience to the law nearly caused tragedy to befall the Kuchiki family and the Soul Society as a whole. Byakuya proved his renewed commitment to the people dear to him when the time came to fight the Arrancars. He covertly allowed Rukia and Renji to join Ichigo's team to rescue Orihime in the palace of Las Noches, despite Captain-General Yamamoto's orders. Byakuya had a very specific reason for fighting the 7th Espada, Zommari Rureaux. Byakuya didn't fight him out of duty; he slew Zommari because that Espada had tried to take Rukia's life, and the way Byakuya put it, Rukia was his pride and joy.
Byakuya's transformation took another step in the war against the Wandenreich, the Quincy empire. He'd grown complacent after suffering defeat at the hands of As Nodt. Humbled, Byakuya underwent more training once he healed, and he took this chance to take a step back to renew his relationship with his zanpakuto Senbonzakura. He wasn't entitled to be the best -- he had to earn his power like anyone else to become Senbonzakura's true master. Byakuya apologized to Rukia and Renji when he fell to As Nodt the first time, and he made up for his defeat when he guided Rukia in manifesting her bankai, Hakka No Togame, in the final fight against As Nodt.
In his worst days, Byakuya was practically a thuggish tool, misusing his elegant sword to create misery. But later, Byakuya learned the way of the hero: faith in others and oneself, the guts to do what's right no matter what others think, and loyalty and commitment to friends, family and loved ones.