Kiss wa Shigoto ni Fukumimasen! Kimajime Ouji no Amai Mitsuai

The kingdom of Remshine is ruled by a royal family with magical powers.
Sophie, a commoner girl, was summoned by the breathtakingly handsome Prince Julien to come to the royal capital. To her surprise, she turned out to be the perfect "sleeve," the partner he needed to utilize his magical powers. Sophie reluctantly agreed to cooperate with Julien, but in order to release their magical powers they had to "make intimate contact"! They kissed as they exterminated demons, and might even have to go further than that...?

(Source: Ohzora Shuppan, translated)