SHITSUGYOU KENJA NO NARIAGARI: KIRAWARETA SAINOU WA SEKAI SAIKYOUDESHITA

Karna was a boy that was given the title of "Sage" from heaven, is scouted by the hero party that had great expectations for his skills. However, his skill "necromancer" was creepy and he was immediately exiled. Karna, who got lost on the road without getting a reward, had accidentally invaded the Demon King territory and was targeted by the demons! Karna faced a demon with a mighty power, but defeats it with magic that overwhemed it by far. A fearsome demon. Meanwhile, Cecilia the devil, who saw the whole scene, offers Karna a large annual salary. And Karna decided to become an enemy of humanity as a magician with the Demon King army… — Description from AniList community (anilist.co).