Hey just to give you a bit of a rundown on my post, highlight the black after you've read it lol.
the idea comes from DDD when Riku jumps into Sora's head to fight nightmare ventus, but done using my hyrbid's ability of possession. Trace is pretty much trying to help Cal tame Dante, but it requires Dante to be active. Essentially what this means is your heartless is actually going to be put into a position of making an active decision to protect you, from my heartless who's trying to eat her lol.
Alsoooo the kiss was just for dramatic effect, once you took in Trace's blood the time limit to possess Calpurnia/Send Anti into her heart started. I just thought it was devious to do