Jirachi

Ah, yes. Jirachi. The hostage. The MacGuffin. The extremely overused plot device. Let's grab him before he screws up, okay?

Personality
Jirachi is kind of an ass.

He's ageless, extremely powerful, and borderline immortal - but he's also been awake for only a few months of his existence. When he goes to sleep at the end of each week, everyone he talked to last time dies and he's presented with an entirely different world when he opens his eyes again. Caring about the mortality of others would be pointless and depressing and his own survival is pretty much guaranteed as well. The only option left is his own amusement, and so he does absolutely everything to maximize this.

He's surprisingly fair within the rules of his own games (wouldn't be fun otherwise), but this just makes him more dangerous. He hasn't granted Luxray any wishes yet, but if she manages to wake him up and win a game, he'll consider it his duty to grant her whatever wish she wants. Even if it ends up screwing himself and the rest of the universe over.