I had this sitting around since I apparently didn't hit the submit button.

Threadjacking: Asking first would be cool, for either me or the person the thread/entry belongs to, but usually I'm cool with it!
Flirtatious advances/Intimacy: If she ever wanted to, sure. Yuuka might be a little bit playful, but she's not easily one to fall in love unless you're a flower.
Fighting / Injuries: Link is free to fight Yuuka! Yuuka doesn't mind having a fight now and then, so it'd be totally cool whenever. Yuuka doesn't really get serious though, but if you wanted to have Link injure her, slicing parts of her is fine.
4th Wall: Nope! She'll mislead people, but she doesn't know anything and nor do I, so I won't slip anything in. \o