Sensei entering play trait: "After [sensei] enters play: Discard all your other Sensei Personalities."
Blood of the Preserver text: "Remove them from the game; ... After the next turn begins, each unit enters play in its owner's home, ignoring costs, restrictions, and entering-play effects;"
I have one sensei in play and one in provinces on my turn. During my attack phase, I use Blood of the Preserver and remove my in-play sensei from play. During the subsequent dynasty phase, I buy the sensei in province. My opponent's turn begins, and Blood of the Preserver returns the first sensei to play.
Do I now have two sensei?