Chi ni Ueta Hanayome wa Ou wo Kurau

In a war-torn world, Kate, a princess-priestess, gains the power of the progenitor vampire to protect her kingdom. Fearing future threats, she proposes a contract marriage to Luka, the king of the continent’s greatest nation, offering her power in exchange. However, Luka despises vampires and treats her coldly. As their unwanted marriage begins, Kate’s vampire instincts awaken uncontrollably, binding them together in a dangerous relationship caught between duty, instinct, and the possibility of love. Source: MU