Board Thread:Fanon Canon/@comment-2089817-20151116044304/@comment-2089817-20151116203239

Senjumaru is a tricky one imo. The 12th Division uses a Shutara Scale, which should alone suggest that she was a former 12th Division Captain, but keep in mind that the 12th Division's specialty in research and development was not an actuality until Urahara's time. Mayuri came right after him. So this suggests that the 12th Division may have had a different focus at first.

Personally, I picture Shutara as the 3rd Division founder, but I have nothing to base that on.