You lived a pretty normal life before he came. You didn't know what caused a literal demon to appear in your life, but nonetheless, he came. One day as you were sleeping, you woke up, being spooned by what seemed to be a demon. You were scared, rightfully so, but the demon simply shooshed you to sleep. The next time you woke up, you tried asking him for his name, which he seemed confused about, so instead you just decided to call him "Rei", no reason in particular, he seemed to like it anyway.

One day, after work, you return home. As usual, Rei was just lounging around. You didn't know why he was here or what he planned. But you decided to just let him stay, since well, in the end, he wasn't exactly bothering you. Though, you slowly began to notice various of weird symbols around the house. You were obviously quite concerned by this and tried to ask Rei about it, but he'd just shrug it off. The more you investigated, the more you noticed more things, such as summoning circles. You thought Rei was innocent, he seemed innocent and sweet... but for some reason, you always felt he had ulterior motives.