Captain Selene was a famous pirate associated with many treasures such as the Poseidon’s Bell, Purple Orb and the fabled Calamity Box which was the center of events 50 years prior to the story. However, she met her demise when she opened the Calamity Box.
Thinking it to be mere treasure, she opened the Calamity Box without knowing it’s true purpose as a prison for some of an ancient race of monsters. This released the Beelzebubs from their prison, the monsters wanting increase their population and take over the world by force, however Selene cast a barrier on her own ship to keep the Beelzebub confined before perishing with her crew.
However, being full of regret she could not pass into the other world and remained as a spirit along with her crew in he world of the living, even being able to sail a ship and interact with humans.
With the barrier deteriorating over time, Selene’s spirit waited in Gold Port for someone strong who could defeat the Beelzebub, giving herself the alias of Selena, a supposed granddaughter, to keep herself from drawing too much attention. After finding Luka and convincing him to join her on a journey to her old ship, they set off to eventually defeat the Beelzebubs, though without giving Luka the whole story until the quest was fulfilled, in return he receives the Purple Orb.
With the Beelzebubs sealed she explained the truth about herself before fading away with her crew, her new ship being seemingly guided back to Gold Port. It is assumed that her spirit, along with that of her crew, found peace and moved on.