A man named Yōki dies in a traffic accident and is reincarnated into a fantasy world, but not as a legendary hero or a demon lord. Instead, he becomes a powerful demon serving as an underling in the Demon Lord's castle. When a party of heroes attacks the castle, Yōki easily defeats them. As he prepares to send the unconscious group back to their town, he notices the party's priestess, Cecilia, and falls in love at first sight.

Rather than harming her or her companions, Yōki confesses his feelings to Cecilia on the spot. She is initially horrified and rejects him, finding his approach invasive given the circumstances. However, he explains that he was once human and has no desire to be evil. Cecilia challenges him to use his great power to help others instead of serving the Demon Lord. Inspired by her words, Yōki allows the hero's party to proceed and kill the Demon Lord. He then removes his own demonic horns and wings to pass as a human and begins a new life as an adventurer in order to get closer to her.

The series follows the unusual and awkward romance that develops between a reformed demon and a principled priestess. Cecilia, who is kind and intelligent, remains wary but eventually agrees to give Yōki a chance, leading to a genuine bond between them. Yōki must navigate his intense feelings while respecting her boundaries, a task made more difficult by the many other suitors vying for Cecilia's attention, including the hero Yūga. The story also explores the political fallout following the Demon Lord's defeat, as the human kingdoms that once united against a common enemy begin fighting amongst themselves.

Key members of the hero's party include Yūga, the party's leader, and the sorceress Mikana. Other characters from Yōki's past as a demon, such as his former subordinates Duke, a Dullahan, and Seek, a Pixie, also appear. The series features a mix of comedy and fantasy action, with notable narrative arcs including Yōki's initial confession, his attempts to date Cecilia, and his efforts to keep his true demonic identity a secret while navigating the politics of a world without a Demon Lord.

The television anime adaptation, produced by studio Gekkou and directed by Tomonori Mine, premiered in January 2026. The series is based on the light novels written by Suisei and illustrated by La-na, which were originally published online starting in 2013.