Bound

Every human being is born bound to a spirit. It is a system set up by the gods to prevent genocide. Most humans are bound to a low level spirit, like a fairy or a ghost or a sprite. Some humans are bound to stronger spirits, like angels, or reapers, or elementals, or demons, however getting bound to a demon is rare. When a human turns 12, they perform a test that reveals a human’s spirit. Most get low-level spirits, some get elementals, however, that is not the case for our protagonist.
Emery Stone was the only spirit-less being in a world where your existence is determined solely on how strong your spirit is. Now, 5 years later, she is disowned by her human parents and adopted by a powerful forest guardian, attending a low-class high school with only one friend, wanting only to live a peaceful life, only for a powerful demon spirit to appear out of nowhere one day claiming to be her Bound Spirit?! How dare he!