Lucius

He is called an Fallen Angel by the order because he sided with the Mamono after the new Demon Lord took over.They sealed him in a prison they used for their most heinous criminals.After 750 years he was released by some humans that were exploring the prison.Instead of leaving the island he claimed it as his home and let it be known that it would be a sanctuary for human and mamono couples(only to Mamono and Mamon friendly humans).There is a port town that is the only safe place to land a ship for exploration since one side of the island has high cliffs and the other has many whirlpools.