Sōjirō Kusaka is a former friend and rival of Toshiro Hitsugaya during their time in the Shinigami Academy and the main villain of Bleach: The DiamondDust Rebellion.
After Kusaka was enrolled in the Shinigami Academy, he met Toshiro Hitsugaya, whom he quickly befriended. Viewing Hitsugaya as a genius, he strove to outdo him and worked constantly to become a good Shinigami so as to protect the Soul Society. Later when Kusaka met his Zanpakuto spirit, Hyorinmaru and gained his Zanpakuto, he found Hitsugaya had met the same spirit, gaining the same sword. Overjoyed at their having the same powers, they became even closer to each other. However the Central 46 ruled that there couldn’t be two Shinigami with the same Zanpakuto, since it was against the Shinigami’s laws. The situation could not be permitted, despite Kusaka and Hitsugaya not intending to violate the law. Hitsugaya didn’t want to fight his friend and offered to give up Hyorinmaru, but the Central 46 forced them to battle for honor of wielding the Zanpakuto, Finally Kusaka cried out he wanted the Zanpakuto for himself and drew his sword, attacking Hitsugaya. This cost him victory since the fight was about who would draw their sword first and as they fought, the Central 46 decided Hitsugaya was the one worthy of Hyorinmaru. Before the fight ended, Kusaka was sentenced to death and numerous special forces appeared on the battlefield. Some restrained Hitsugaya, while the others surrounded Kusaka, stabbing him through the chest and one of them finally finished him with a strike to his head. As his Zanpakuto dissolved, Kusaka asked why he had to die since he’d fought for the Soul Society. His execution was kept secret with his academy records getting destroyed and almost everyone in the Soul Society came to never know his existence. However Kusaka was reborn by the Ōin, ending up in Hueco Mundo, where he gained the loyalty of two Arrancar, Ying and Yang.
Kusaka returned to the Soul Society, determined to have revenge and plotted to steal the Ōin, so as to rule the Soul Society. He had Ying and Yang assaulted the group transporting it and in the confusion, appeared before Hitsugaya, who’d been assigned to protect it. Kusaka stabbed him in the stomach then disappeared, prompting the captain to leave his post to try and find him.
After captain Shunsui Kyoraku began finding out about Kusaka, the rogue Shinigami attacked him. He used Hyorinmaru’s freezing powers to hurt the captain which led the Soul Society to believe Hitsugaya was a traitor. Kusaka and his minions went to deal with Ichigo Kurosaki and Rukia Kuchiki, attacking just after they were told about the rogue Shinigami’s identity. They fought briefly until Kusaka froze Ichigo, then left Rukia to Ying and Yang while he went looking for Hitsugaya. He asked if the captain becoming a Shinigami had all been just for Momo Hinamori, but Histugaya demanded he leave her out of this. Kusaka then used the Ōin’s power to teleport them to Sokyoku Hill in the Soul Society. He then told Hitsugaya to cut the Ōin with his Bankai, but he refused and the forces of the Soul Society arrived to capture the pair. But Ichigo and Rukia arrived and stopped them with Hitsugaya attacking Kusaka, surprising the Shinigami. Ichigo explained that the captain had left because he wanted to settle things with his former friend, but didn’t want anyone else to get hurt. Using the distraction, Kusaka cut the Ōin himself, unleashing its power and transforming him into an enormous ice dragon form, becoming like a god. In this new form, he succeeded in easily countering an attack from Kenpachi Zaraki and
remarked his new power was incredible. Kusaka landed on a large building and merged with it, “taking root” and encasing it in ice, eventually becoming an enormous ice tree. As the Shinigami approached via the branches, Kusaka shattered it, but since
he had not mastered his Bankai at that point, he lost control of the Ōin’s power. This resulted in a rapidly expanding hemisphere, inside which Kusaka created a castle for himself, where he stood immobile. From the castle, numerous Hollows spawned forth with the same regenerative power that Kusaka had gained. The rogue Shinigami proceeded to create an enormous force-field, which started destroying the Soul Society. Most of the Shinigami were trapped outside with Ichigo and Hitsugaya being two of the exceptions. Renji Abarai and Ikkaku Madarame used their Bankais to open a path for Ichigo and Hitsugaya to ascend the ice tower.
A number of ice dragon heads attacked them, but the captain dealt with them while Ichigo attacked Kusaka, who countered with an energy blast. Hitsugaya managed to stun his former friend, allowing Ichigo to drive his sword into his head, then unleashed a Getsuga Tenshou, defeating him. As the Ōin returned to normal, Kusaka’s ice dragon form dissolved, leaving him in his old form.
He and Hitsugaya charged at each other one last time to finish their battle with the captain emerging the winner after he stabbed him in the chest. Kusaka said he would never die and Hitsugaya said they would always be friends as Kusaka faded, leaving his broken Zanpakuto and cape behind.
Kusaka was once an idealist, determined to defend and uphold the ideals of the Soul Society. He was very close friends with Hitsugaya, until his execution, which has now made him bitter and determined to have revenge. Kusaka is also obsessed with the power of the Ōin due to it bringing him back and wants to use it to rule the entire Soul Society. However in the end, he seemed to return more to his old self and Ichigo said that he and Hitsugaya weren’t so different, since all he wanted was to finish their fight as well.
Kusaka has a great amount of spiritual power that is apparently on par with a captain. He has demonstrated
enormous skill in both swordsmanship and Shunpo, a technique that lets him move extremely fast, able to keep up with masters of it. Kusaka possesses the Zanpakuto, Hyorinmaru, and he can release the Shikai form of it with the release command, “Sit upon the frozen heavens”. When he does so, Hyorinmaru becomes larger with a crescent shaped blade on the end of a chain attached to the end of the hilt. In Shikai form, it gains the power to control ice and water and when Kusaka slashes with it, it generates flows of ice that resemble Chinese dragons. The chain blade can also freeze anything he traps with it.
After releasing the power of the Ōin, Kusaka was transformed into an enormous dragon made of ice, becoming even more powerful. In this form, he gains enormous strength and durability, as well as the ability to regenerate his damaged body. Kusaka can fire ice projectiles out of his mouth as well as generate ones that resemble dragons, like the ones he generates with Hyorinmaru. He can freeze what he comes into contact with and when the Ōin went out of control, he created his own dimension. Inside it, Kusaka could summon a large number of Hollows and resurrect any of his forces that were struck down. He can also fire a powerful energy blast from his mouth, which was strong enough to stop Ichigo in Bankai with his Hollow Mask.
- Despite having the same Zanpakuto as Hitsugaya, Kusaka’s version of Hyorinmaru has a few subtle differences from Hitsugaya’s version. His has a dark red sheath while the captain’s is blue, the blade is more standard sized and the guard is more hollow with outward curved points. Also the ice Kusaka’s version of Hyorinmaru generates is a light purple color as opposed to Hitsugaya’s light blue.
- Kusaka has appeared in the video game Bleach: Heat the Soul 5, 6, and 7 and Bleach: The 3rd Phantom.