Kekkai Genkai user, * it probably is then.

I was thinking it would be Ajisai or maybe even Karui, hoping it wouldnt be a ninja we already have in game. (And I have 4 star)

Ajisai doesnt have a kekkai genkai, which is the 2nd clue. If you go to the combo simulator and then go to blood line limit, then females: your only options are the Hinata versions (which I wouldnt mind Hinata [Cloak] cause breakthroughs), Guren, Kurotsuchi, Mei, Pakura, and Hanabi. Out of all of those Guren also fits the theme of a ninja that gets more abilities the more stars you get (with her getting a dodge at 3 stars and an enhanced mystery at 4).