Romulus is a Cannon Fist user and the vice captain of the Mantle Pirates.
Romulus also has a backstory, The Plight of Romulus, found in a book in-game.
Once boarding the randomly appearing Rumbling Caldera, players are able to fight Romulus.
Borealis Heavy Shot
This is the move where Romulus launches a large cannonball at you. The cannonball creates a giant splash in contact with water. It also makes a very loud noise that sounds like a mortar shooting Borealis 300 lb cannonballs. This attack allows him to quickly destroy any boats nearby. This attack only occurs when the player is in the Rumbling Caldera's vicinity, but not when the player has boarded the ship.
This move deals around 2,000 damage.
Romulus throws cannonballs at the player, dealing 156 damage. This only happens when the player is near Romulus.