Senna claims to be a shinigami, but it's unusual that shinigami still contain their memories when they lived. Urahara finds out about her memories, and talks to soul society. Once the Soul Society was researching her, they find out that she is not a shinigami, but a part of what they call Blank, something that contains people's memories when they were alive. Some captains of the Gotei 13, especially Captain Yamamoto, goes to the real world and retrieves Senna, fearing that her existence is a threat. Apparently, a former noble family of the Gotei 13, is after Senna, using her to get revenge at Soul Society for punishing them centuries ago. Ichigo is going after her, but he cannot save her alone. Because the captains have different opinions, they split up to either go with Ichigo or to stay in Seireitei and follow Captain Yamamoto's orders.
