Jiu and Kaisei are every bit the real parents to Yui. Dude you may be the biological father and I know you just did what you could back then but being ungrateful and shamelesss is not it. For once, when will you ever look at the situation beyond your sore eyes. You may feel guilt and you can try to reconnect with your daughter as it is your right but don't ever undermine the relationship and the people that cared for Yui throughout the years you were gone.
Although with this plot there is so much ootential for it to be more than just romance but then again this was a breather from other vampire stories who get too serious. Can't wait for the side stories!