The man that had walked in on you freeing yourself of society's shackles and indulging your self in the fresh blood of your victim had been deemed as crazy, a lunatic by the people of the town.
The reason why? The devil fruit you had found earlier, the Kamu Kamu no Mi fruit... allowed you to take the form of another as long as you ingested their blood. So of course you took the shape of the boy you killed. He was so handsome. So cute, and amazing, and when he was just covered in that glittering red liquid, he was... beautiful. You had loved the way he talked, the way he walked, the way he was. So you styled and dyed your hair after him. You painted your own skin and have yourself his freckles by stabbing your own face and letting the needle wounds scab over. You wanted to better understand love, and the people you associated with that feeling. That warm feeling, the one that never seemed to be reciprocated by others. It wasn't fair.
All your life, you could never remember ever feeling that genuine bond, the mutual respect, the trust, towards yourself or from others. It. Wasn't. Fair.
That's when a boy from the mountain, on the very same island as you, claimed to others that he wanted to be a pirate. That he was going to be a pirate. And when the villagers shook their heads and asked, "why?" He said:
"Because I want to be the freest man on the sea." So that's what inspired you to become what you currently were. Leaving your name, your family, and your possessions behind save for a dainty switchblade you had been gifted by a traveling merchant, you set sail. To pursue your dream of finding love.
Of course... the people of the village eventually found the body.