OUT OF CHARACTER
Backtagging: Sure. I'll be doing a lot of this myself due to timezones (GMT). If it's a thread I've left for a few days and I've not responded, and you want to finish it up, just prod me. Chances are something came up and I was distracted from it.
Threadhopping: Usually, yes! If it's filtered/private/reserved use your own judgement here.
Fourthwalling: No thank you.
Offensive subjects: Rape, excessive gore/torture/horror themes. Otherwise I'm mostly game. If it's something potentially risky please ask.

IN CHARACTER
Hugging: Serah's not overly touchy-feely, but she will hug you if she knows you. She's usually quite loving and affectionate, so it's more likely than a lot of other characters. If you hug her, she will most likely accept it happily, unless she doesn't know you particularly well, then she may not act in kind.
Flirting: She may be coy in response, depending on who it is and the situation, but most of the time she'll shut it down. Sorry boys, she's married.
Kissing and/or other intimate actions: Is your name Snow Villiers? Yes? Congratulations! Husband gets all the kisses and the snuggles. ... as an aside, my take on Serah/Snow: despite fandom's insistance and ofen tearing apart of Snow's character to make Serah/Noel work, there is nothing to point towards them canon-wise and Serah still loves Snow. That's my take on it, regardless of the fact I ship Snow/Serah. Just so you know.
Fighting: Feel free to randomly start a brawl with her. She'll defend herself, and you'll most likely get a run for you money. No more miss nice girl.
Injuries: Discuss? Bruises are fine, anything that involves broken bones or loss of limb please ask.