Aizen modified the Arrancar Wonderweiss specifically to seal Ryūjin Jakka, Yamamoto's Zanpakutō. After Wonderweiss was killed, the power of Ryūjin Jakka was about to be released from his body in an explosion. Yamamoto suppressed the explosion with his body and was thus injured. He then used Hadō 96 Ittō Kasō to attack Aizen, sacrificing his arm in the process. Aizen, however, survived.