Board Thread:General Discussion/@comment-25227771-20140926065953/@comment-5398287-20140926193233

Technically, any soul can learn Kido, as seen with Kukaku Shiba. However, given that her four known techniques possess theoretically limitless power based on the strength of her resolve (which has steeled up enormously, judging by the Fullbring arc), I don't think she really has a need to do so.