Once there was a tribe who knew the powerful magic of illusion, this magic has been lost and can’t be learned by people that aren’t related to the tribe.
They were raided at night by pirates whose names have been lost to history and they took over the land with their powerful magic. The tribe escaped and traveled the sea, but they were being chased by the pirates. They found a island and landed there and quickly used all there magic to create the dark seas so they could hide from them.
The pirates entered the dark sea, they were terrified at what they saw, monsters where everywhere and dark images of wizards started to attack their boats. They tried to fightback but they all died and now roam the seas as spirits trying to attack people to steal their boats to escape.
The tribe’s island was safe and they hide within the dark seas never to be messed with again.
(Feedback on how to make this better will be nice)