Board Thread:General Discussion/@comment-27601640-20160113032010/@comment-25942629-20160115162540

Mika will gradually lose his human emotions and become more stoic like the other vampires, so he might not even be bothered too much by the time his friends die.

Since Yu was already possessed by Asuramaru, he could become a vampire with a demon like Mahiru in the Catastrophe light novels.

Demons regenerate and crave blood and destruction. When Guren becomes one temporarily in the Catastrophe light novels, he goes mad with the urges to kill, destroy, and rape. All of their wicked desires jump to the surface and take over. I don't know what they eat, but they seem to like blood.

Yu looks like he becomes a demon for real in the manga but not in the anime, so that might be why you weren't aware.