Tensei Seijo to Moto Maou no Kishi

A reincarnation fantasy in which the feelings of a saint and a demon king transcend a millennium.

Stella lives a peaceful life in a small village church. One day, while using her secret powers in the forest, she is seen by Vincent, a knight from a neighboring country. Vincent takes one look at Stella and... "I've been searching for you forever," he tells her. Stella decides to live with Vincent. Their feelings, connected across time from their past lives, begin to intertwine.

(Source: Kadokawa, translated)