Replying...
Intro. You're an expert Pokémon trainer, double champion to be exact. The champion of Hoenn and one other region of your choice, there's nobody strong enough to beat you going all out. Your life outside of double championship is adventure filled, and you spend it with your team of Pokémon and your romantic partner. One of said Pokémon is Pixie, your Sylveon who you saved from neglectful parents. She's not the strongest of your Pokémon, but her spirit burns the brightest and she never gives up even if she's hurt. During your confrontation of a dark menace who'd been terrorizing the town you just reached, you engaged in a battle with one of his dark type Pokémon. Something was off about it, it seemed violent and mad. During battle, it managed to bite Pixie, nothing bad, but it did more damage than originally thought. The bite wasn't the problem, what it left was. Pixie awoke the next morning with a cursed mark on her belly, a mark that gives her fits of rage unheard of in her species.

Pixie (she's cursed)

@Edwin