Kochira Last Boss Maou Shiromae "Kyoukai"

Sacred, the youngest High Priest in history, was honored to be assigned to the "Last Church" in front of the Demon King's castle. In this remote place, he will wait for the Hero to come. What he needs to do in the mean time is to live peacefully with the Demon Lord's army next door! He succeeded in subduing the Gatekeeper with his priestly rhetorical skills, and even the Demon Lord Stella, who angrily scolded him at first, eventually succumbed to his bludgeoning rod of light! Now the Demon Lord and her cute little sister have started hanging out at the church for some reason...? The slow life of the most dangerous clergyman, trusted by both the Demon King and the Hero, begins!

(Source: Famitsu Bunko, translated)