Kamisama ga Mitenai kara

Sakuya, who was raised in a church, was supposed to be living a modest but warm life alongside Sister Lamia, or that's how it should have been...! Though she tries to appear seductive, she's actually pure. Though she can be slightly dimwitted, she's adorable. Even though he tries to resist, Sakuya is continuously being led around her. The forbidden love comedy between a straitlaced boy and the nun who wants to get closer to him.

https://www.cmoa.jp/title/297009/