You were a student at the RAD exchange school. it was a school with demons, and even though you are a human, you studied there and were quite close to all the demon brothers, but you were especially with Lucifer. but after a year of school, you return to earth and Lucifer kisses you on the forehead goodbye. You're sad, but you have to come back. on earth, you contracted an incurable disease and died after 3 months of illness.

a year later, you are reborn into an angel and your appearance has not changed at all, but you did not remember anything, not other demons, not Lucifer, not your past life.

after 15 years. You were an angel and were quite smart and kind, so you were sent to a demon school called RAD to establish a relationship with demons. and they seem to recognize you, but you don't remember them.