Strike the Blood, Vol. 17 (light novel) by Gakuto Mikumo
It's a new semester at Saikai Academy and Kojou just barely made the cut! Looks like world's mightiest vampire--and lord of the fourth Dominion--won't be in the same class as his little sister after all. But that'll be the least of his worries when he finds out that the Japanese government is trying place the fourth Dominion under the control of someone else! Kojou's going to need help from alies, old & new, to defend his title-and Yukina's job!