Fairy Tail: The Demon King

Fairy Tail: The Demon King,

Two children separated when their home is attacked, two orphans who take different roads in life, one who was captured as a slave becomes one of the beacons of light, a queen of fairies, while the other one who escaped, becomes corrupt with darkness and evil, a demon king

This is the story of the reunion between the beacon of light and the bringer of evil