There Was a Cute Girl in the Hero's Party, so I Tried Confessing to Her - Yuusha Party ni Kawaii Ko ga Ita node, Kokuhaku shitemita.

Synopsis

Yoki was once a human but reincarnated into a demon. He now holds a middling position serving the Demon King tasked with taking down the hero party. But when he finally faces them, Yoki thinks... ""No way… she's perfect."" Of all things, he fell in love at first sight with Cecilia, the priest of the hero party! Her serious gaze, her every little gesture—everything about her is too cute! She's an angel! And so, Yoki made up his mind that he would confess his feelings to her.