This is the story of Megumi Sakahata, who is a fallen angel. He was banished from heaven because he had one black wing and one white wing; the head angels were unable to kill him due to his one white wing. They always killed black-winged angels when they arrive; little realising that only the purest of souls can become black-wings, as they call them. Megumi was one of the few angels who are unable to be determined as entirely pure-spirited or not. There is only one black-wings allowed to exist at one time, the one who works for Death; the Grim Reaper, as some call him. That black-wings is the messanger of Death.
So Megumi is sent to Earth to live with his 'deformed' cousin. By 'deformed', the white-wings mean a half-breed angel; black and white wings. He goes to school one day, like normal, but when he returns, his cousin has a surprise in store for him!