I don't know, but that vampire girl seems to me to be an OP female version of kenji of sorts. Not as devious as Kenji, but still already thinking Yuki is her's & even planing on having babies with Yuki already. 

No wonder Yuki is having those shivers run thru her body lol.

Thinking on making her an empress, but Yuki is more into saving & revenge for Nana & her clans & getting stronger to move to the next realm, so no use being an empress i would say.

Yuki might pick up more wives, but I reather think Nana is her one & only soul linked mate.