Why Tho?

All vampires have secondary genders, so that means you're either an Alpha, Beta, or Omega. With his luck, Mika is an Omega.
After they defeated the vampires, they kept Mika alive on Yuus request, but he has to get a weekly injection to keep his bloodlust under control.
Back to him being an Omega, Mika goes into heat, which no one knows what to do. So Yuu does the dumbest thing ever and grants all that Mika wants during the 7 days of his heat.
Vampires can't get humans pregnant, but how people wish they could say the same for the other way around.