An artifact known as the "King's Seal" is stolen during transport from the Soul Society by an unidentified Soul Reaper and two Arrancar resembling girls who control fire and lightning. During the attack, Tōshirō Hitsugaya corners and seems to recognize the Soul Reaper, who immediately stabs him in the stomach. In the middle of battle, Hitsugaya abandons his post to pursue him and leaves his squad behind to fend for themselves. After the battle, Soul Society suspects Hitsugaya of treason and orders his immediate capture. The whole 10th Squad is then put on house arrest at which time they can surmise whether or not the division should be abolished.

With the whole of Soul Society looking for Hitsugaya, Ichigo as a soul reaper on patrol accidentally stumbles upon Squad 2 Captain Soifon while she is conducting an investigation of the transport site. Soifon informs him of the events happening in the Soul Society and dispels the kido surrounding them. As Soifon disappears with her crew, Tōshirō makes his presence known and passes out in front of Ichigo and Uryu. Awakening in the Kurosaki residence, Tōshirō refuses to explain what's happening. In the midst of their discussion, Ichigo is attacked by the two arrancar before he can force the issue. Tōshirō escapes, continues to avoid capture, and things only look worse when the Soul Reaper thief, identified as Former Soul Reaper Sōjirō Kusaka, uses Hyōrinmaru, a sword identical to Hitsugaya's, to injure Shunsui Kyōraku. Tōshirō's capture is then made top priority and his execution is approved.

Meanwhile, back in the human world, Rukia has caught up with Ichigo. The gang exchange information, and Rukia reveals rather surprising, in-depth knowledge of Hitsugaya's personality, as well as some rather accurate guesses as to what Hitsugaya plans to do next. During the talk, Ichigo realizes what might be troubling Hitsugaya and leaves to find him.

Through his wandering to avoid capture, Tōshirō eventually manages to track Sōjirō down, where it is revealed that the two managed to manifest the same zanpakutō. Because it is impossible for the same zanpakuto to be wielded in Soul Society, the two were forced to fight to the death. Tōshirō did not wish to fight, but was left with no other option as Kusaka attacked, claiming that he was the only one worthy of Hyōrinmaru. In the fight, Kusaka is dealt a serious wound. Before the battle could be decided, the Military Corps carried out his execution. Cursing Central 46 and Soul Society, Kusaka died and was reborn in Hueco Mundo, where he became a hollow and started his plans of revenge against the Soul Society. Once he learned of the King's Seal and its powers, which allows the user to freely manipulate time, space, and matter within a small space, he leapt at the opportunity to settle the score with both Hitsugaya and Soul Society.

Using the King's Seal, Sōjirō teleports Tōshirō and himself to Soul Society, needing the power of Tōshirō's bankai to break the seal. When Tōshirō refuses, Sōjirō breaks the seal himself, having learned bankai himself with the help of the King's Seal. However, because he lacks the control which Tōshirō possesses, the power goes berserk and threatens to destroy both Soul Society and the real world. With much help, Ichigo in his Visored form and Tōshirō manage to destroy Sōjirō's dragon-like bankai form. Returned to his regular form, Sōjirō and Tōshirō have one last clash. Kusaka is defeated and dies, finally understanding that he really wasn't worthy of Hyōrinmaru. In the end, Tōshirō is cleared of all charges and the King's Seal is restored, allowing Tōshirō to finally put his past to rest.