Originally Posted by
Dark Soul # 7
It beefed his strength up to the level of casually stopping Komamura's bankai attacks and gave him a pretty potent healing factor.
The only reason Hisagi got in a good blow was because Tousen got careless since he regained his sight. And that's not what killed him, which is pretty impressive since Hisagi released his shikai inside Tousen's head. Tousen died from exploding due to... it's not clear why he exploded... kinda implied that the hollowfication was just too much for him but it's never clarified... Komamura seemed to blame Aizen for it.