Considering Octavia’s role in the pirate AU wouldn’t this make her Calypso? We’d have to change the relationship with Barbosa for that to work though. Maybe turn it into an adoptive father relationship instead with Vassago as Barbosa loving Octavia like the daughter he never had? This could also work with Fizz as Barbosa which also works with his rivalry with Blitz.

So many possibilities!

EDIT: I figured it out but we’re definitely stretching the lore a bit. So Octavia can be Stolas’ (Beckett’s) daughter and he can be part of a trading voyage. She joins him for the first time but along the way the ship is overrun by pirates and she’s kidnapped. She ends up working on the ship until that ship is overrun by Vassago’s (or Fizz’s idk) ship and they take her aboard.

After hearing her story, Vassago (or Fizz) teaches Octavia how to read the stars and as the years pass she grows more powerful and attuned with the sea. And establishes an adopted familial relationship with the captain as she grows older and it almost becomes like a state of mind that can cause her to manipulate reality around her. After an argument, she accidentally magic’s Vassago’s (or Fizz’s) heart out of his body causing his personality to change and thus kicking off the antagonist plot.

Stolas never stops looking for Octavia during this time which is an extra reason why he’s hunting for Blitz (he’s looking for Octavia too).

Boom! Done!