This Girl is a Little Wild

In a battle with the Demon King, the captain of the Holy Knights got his soul trapped within a weak girl’s body. Upon waking up, the captain finds out that the girl is in danger. In order to protect himself, he decides to head to the church to prove his identity, but to his surprise, he meets the blah blah blah blah captain of something, and became his fiancee. Can she really prove her identity? Also, what will happen to their relationship?