The Pirate Prince

The Pirate Prince is the most dreaded pirate to ever sail the seas. He made such a name to himself that he became a legend while still alive, and his name was whispered in fear even after he abandoned piracy.
The Pirate Prince was a young man named Kouji. He was a bastard son of King Temeru of Ikkoku, though his birth circumstances were not known until after the king's death, when Kouji officially received the title of prince and gave up piracy to live in the castle with his mother.
(This means the Pirate Prince was not called such while he was actually out there pirating. The nickname was given to him after his "retirement" as a more catchy way to spread his fame.)
Kouji's desire to pillage the seas was born out of need for revenge against his father. As a child, Kouji grew up with his mother telling him stories of how King Temeru had tricked his mother with a fake marriage proposal. She thought she was going to be queen, but was in fact sent away and threatened to be killed if she ever approached the castle or told about Kouji's real parentage to anyone. He and his mother grew up in poverty because of the king's heartlessness, so he vowed to make the king pay.
Unfortunately for him, King Temeru was killed before he got a chance to even meet him, let alone slice him in half with his sword (as per his original plan). That said, the new queen was elected with the explicit mission of correcting all the injustices perpetrated by King Temeru. She sought Kouji and his mother out and offered them a place in the castle, as well as royal titles. Pirate Kouji became Prince Kouji, and his mother became known as Royal Consort Angelia. He also found out he had two other bastard brothers, each from a different mother, who were also banished and threatened by King Temeru. Queen Mimi brought them all to the castle and the three families bonded over their hatred for the king.

Summary

The Pirate Prince was a dreaded pirate who roamed the seas from an incredibly young age. He took over his first ship at the age of 14, and used it to pillage and sink trade ships from Ikkoku who dared cross paths with him.
His crew was as young as he was. The secret for their success was likely the presence of a skilled Warlock (not a flute player, or sorcerer, or wizard), though the Pirate Prince had a talent for intimidation and unparalleled thirst for violence and blood. He also possessed the kind of emotional intelligence that made it easy for him to traumatise and scare weak opponents and bluff against strong ones. His crew made a point of creating big explosions with lots of fire and noise.
But the Pirate Prince and his crew only attacked ships from Ikkoku, and they made a point of spreading their message as such. They wanted the world to know that the purpose of their existence was to destabilise Ikkoku's economy and take back what the evil King Temeru was taking from them.
Thus, once King Temeru was killed and replaced by the much kinder and fairer Queen Mimi, the Pirate Prince disbanded his crew and became simply a Prince.

Variations & Mutation

Not many people seem to realise that the Pirate Prince was not called this way while he was still a pirate. Everybody knew he hated Ikkoku and King Temeru, but nobody realised this was because he was a bastard child of the king. The name "Pirate Prince" was added to his story later, as a catchy way to make it spread.
It is now not uncommon to see the legend of the Pirate Prince be told not as a pirating story, but as testament to the great changes implemented by Queen Mimi and the rebirth of Ikkoku.