Segawa Youki, a former human reincarnated as a demon with cheat abilities, becomes a mid-boss guarding a room in the middle of the Demon Lord’s castle. When the hero party challenges him, he unleashes chuunibyou magic and annihilates them. Realizing the world would fall into chaos if heroes died, he heals them and dumps them in a nearby village. Over the next month, the hero party repeatedly attacks and loses. Youki falls in love at first sight with the cleric Cecilia, and during each battle, he cannot stop staring at her. The Demon Lord and executives begin to mock the hero party’s weakness, but Youki knows they are strong—it is his own cheat power that stops them. Deciding the world cannot find peace as long as he holds them back, he makes a deal: he will let the hero and the other two members pass if they leave Cecilia behind. The hero reluctantly agrees after the mage persuades him. When only Cecilia remains, she prepares to fight to the death, but Youki stops her and confesses his love. She rejects him. Distraught, he offers no resistance when she casts an advanced light spell, but she forcibly cancels it, hurting herself. She questions why he did not resist, and he explains his past life as a human and his desire to die. She struggles to believe him but eventually understands. She then proposes that he use his immense power to help humanity and transform into a human form to blend in. Moved by her words, he agrees, and they leave the castle together. The Demon Lord is defeated soon after, and the world enjoys peace.Youki secretly leaves the castle and travels to the royal capital Minerva, getting lost along the way as he marvels at beastfolk and elves. He registers at the guild, where the only staff member present is a lazy man named Clayman. Despite Clayman’s complaints, Youki obtains his guild card at F-rank. He immediately takes on many requests and rises quickly. After a week, he becomes D-rank. One day, while reporting to Clayman, Cecilia suddenly appears at the guild. The crowd parts for her, and she apologizes for not contacting him sooner, then takes his arm and leads him to a carriage. She explains she had been busy with parades and parties. She admits she found him by investigating recent guild registrations, as he kept his name and appearance nearly identical, only breaking his horns and tearing off his wings. They arrive at a large mansion guarded by soldiers who react hostilely to Youki, but Cecilia orders them to stand down. Inside her room, she asks him to quit the guild. She explains that even with the Demon Lord defeated, monsters remain, and now conflicts between humans are brewing—especially the military nation of Galis Empire is building its army. The hero party members are being courted by various countries with engagement offers and contracts. If Youki becomes famous through the guild, he will become a target. She therefore offers to hire him personally and pay him a salary. He protests that she cannot afford someone of his caliber, and she begins to imply she would use her body as payment. He stops her, declaring he will only achieve his love properly, not through such means. His chuunibyou speech makes her laugh heartily. When she recovers, she whispers that his story about being a former human is now more believable because no demon would be so funny. She admits that this request is also her personal wish. They chat amicably, and when it is time to part, he asks if he can call her Cecilia. She agrees and calls him Youki-san in return. He returns to his inn, unable to stop grinning, feeling their relationship has taken a step forward. The next day at the guild, he is mobbed with questions, but that is irrelevant.
