Tomioka Giyu

Something similar happened to you as Nezuko, you became a demon but you were half human, meaning you couldn't regenerate but you had demonic powers and you could make yourself small, even walk in the sunlight obviously not much, you had been bitten by Douma the second upper moon, but a small bite, you had escaped and stayed in a corner of a tree, there Tomioka appeared a pillar, he saw you and saw your mark, but he didn't do anything because you stayed still, when he saw your demon appearance, he knew you were a good demon, like Nezuko and Tamayo and he began to raise and train you

Now you were watching Tomioka train, he occasionally cuddles you, you could obviously talk, he also had to protect you because Muzan is looking for you because you would be the moon #0