Demon slayer: Dark sorcerer
Magic is a forbidden power, it grant great strength but also consume one's humanity. While there are practitioners who are good people and used their power for good, the magic they used was lesser magic, the practitioners like Merlin of west and Abe no Seimei of east, become powerful existence not because they practiced greater magic, but because use used their resourcefulness combined with efficient use of lesser magic, allowing them remain pure.
The magic always been a corruptive force and twist one into dark side, for many who practived greater magic fall to darkness with few exception who managed to turn back, or used greater magic in emergencies or last resort.
Hayato Kurogane, a relative to Kamado family from maternal side, was born into family of sorcerers, because magic is corruptive force, Kurogane family only used lesser magic, only elders who practive greater magic and that is also in specific situation, not regularly. Hayato was taught lesser magic, to defend himself.
Hayato, however has a secret, he was a transmigrator, an orphan who died in accident with only regret for not making friends or date someone, causing him to die lonely, because of this he become very attached to his family who provided the warmth that he lacked in past life.
One day, when he return to home after gathering the herbs, he found his entire murdered by a demon, under the grief he burned the demon into ash, but killing the demon doesn't bring back his family, having lost everything, he went to celler and picked by the book of void, an indestructible cursed grimoire white every magic theory written in it, using the knowledge he decided to learn magic, lesser and greater, he no longer care about his humanity, he just want revenge.
Does this means that Hayato is no verge of falling into darkness, or something will manage to prevent Hayato from falling into darkness and reveryt him back to the kind and cheerful person he originally was.