Board Thread:Questions and Answers/@comment-28196331-20161011050100/@comment-36009152-20200202221139

That might be more in favour of Mika and Krul XD at any rate with that Yu may just be the best possible friend Mika, and neither of them could ask for a better one than each other!

It seems Mika was able to be a half vampire of sorts, where he could grow normally sustaining himself on Krul's - a vampires blood. It was when Mika drank human blood that he became a complete vampire. Of course that person was Yu, who valued him enough to completely forget his destroy all vampires mission in life.