I'll keep on with this. Cassi latched onto him because they are very much more alike and also because he is as alone as she feels. He was much more open to her because he hasn't had anyone in his head since the Time War, whereas Ten has been used to having Rose and Dare in his head for years now. Nine was open and vulnerable to it. I'm in the middle of a Zeppelins chapter and a Hunger Moon chapter and will finish those and then write the next one of these.