Go near the right book shelf and do the right sequences and a door will open to a long hallway that leads to a with a special doll. Next to it is a sign that says. "Be cautious of this doll touch it with your zanpakuto, any stage and it will let your zanpakuto's spirit use it as a medium and materialize into its solid form. touch it with your hand and it will transform into your true self but if you whisper come out hollow it will become the medium for your inner hollow. But be warned when your inner self comes out they will be at the peak of your full strength from the moment you touch it also all the beings will never get exhausted/run out of stamina the only way to stop them is to beat them or surrender."