Threadhopping?
Sure, I don't see why not! I'd like it if you cleared it with me and the other person/people I'm threading with, though, just so we have a heads up and in case we need to coordinate fun plot things.
Backtagging?
Ab-so-lutely. Life happens, attention spans suck, plots have to wait, muses are difficult, other RPs demand focus... There are lots of reasons for you and me to be unable to finish a thread the day it technically happens. Backtag away!
Back-dating entries?
If we have to. If it's a big thing that would have a large impact on Xion, I'd like to try to avoid it. I'm always paranoid worried that it'll heavily affect her current mindset, and since I don't know what her thoughts about the situation will be in the end, I don't know how it'll affect her current mindset, and... etc., etc., etc.
But talk to me anyway, because as high-strung as I am about silly things like this, I'm still willing to at least try to work things out. See the last question about IM RP.
Hugging/kissing/other sort of intimate actions?
XD Go for it. If it's something like groping or anything more than that (... if your muse is a pedo creeper...), drop me a line first so we can plot ahead, but if it feels like it comes naturally from the characters, chances are, I'll be cool with it even if it's a bit squicky; it's the muses' damn fault for not having morals -- I mean.
Xion hasn't had a lot of experience with physical contact; Roxas is pretty much the only person who's ever initiated friendly, non-violent contact with her, and that was just hand-holding. She's an ickle virgin! She doesn't even know how to kiss! Hugs and pecks on the cheek and hand-holding will be met with awkwardness and shyness. Anything more than that will probably brainbreak her for a while. Just, uh. So you know.
Punching or causing some other form of physical harm?
Bahahaha, by all means, I love a fight. I can't promise I'm the best at writing fight scenes and I can't promise that Xion won't throw the first punch, but get in contact with me and we can 8DDD about the fight together. XD
Is there anything that should not be mentioned near her?
Uhhhhh. Nope, everything's fair game. There are a lot of things Xi doesn't know about and will have a hard time understanding, as well as a good number of things (like being a replica, not having a heart, being a martyr, etc.) that will make her uncomfortable/unhappy/emotionally keysmashy, but feel free to bring them up anyway. <3 I'm a mean mun.
Is there anything you need us to know about interacting with her (i.e. special physical features or abilities)?
Okay, so this is where things'll get interesting.
Xion isn't psychic or anything like that, but she has a general feel for auras -- she can probably pick out someone's elemental affiliation, if they have one, and if your muse is especially Nothing-, Light- or Dark-oriented, she'll probably sense that, too, but anything past the basics is beyond her. If your muse is particularly powerful, she might get ping'd, depending on whether we want her to or not for plot purposes. (For example, since Kefka Palazzo from FFVI is a god of magic, she'd most likely be able to tell that he's got ridiculous amounts of magic, unless I forget we want her to be a derp, like Soraspawn have a habit of being.)
Xion herself is... very odd, because she's aligned with both Nothing (as a replica) and Light (as someone closely connected to Sora), though more of the latter than the former at this point in time. Pretty much all of that energy/magic is not hers -- it's Roxas's and Sora's, save for the basic amount she needs to function on. If she lost that energy/magic, she would quickly lose power and prooooobably pass out. She's known for doing that in canon, after all.
Xion's entire existence is founded on the links of Sora's memories she absorbed through Roxas. Her own personality was born initially out of Sora's memories of Kairi, and from there she picked up some of Sora's traits simply because, well, they're his memories. Under the definitions of other worlds, it could be said that Xion wasn't born with a soul; instead, she developed one "unnaturally." Even her heart, the core and source of her emotions, is fake -- a false heart created by Vexen, the Nobody in charge of the Organization's Replica Project. Though it's an "unnatural" heart, it functions just as well as any other, though albeit erratically -- but a psychic or anyone who can read into the heart or anything like that will probably be able to pick up on the fact that it's not "real."
Anything else that was not mentioned above?
Xion's a bit of a difficult muse to handwave things with because in order for it to really sink in and affect her, she needs to experience it to some degree. This is because she can be fairly volatile in her emotions and, while I can hazard general guesses about how she'll react to things, I seriously will have no idea how she'll exactly react and feel about something until it happens to her. The details of the situation, from the specific words the characters say to the aura/feel of the thread at the time, have a huge impact on her reactions, emotions, and mood, and she is a very unpredictable muse because of that. (It doesn't help that she is very loud and very alive in my head.)
As such, handwaving things without talking stuff out with the people involved just... doesn't really work. The best way to develop strong and lasting CR with Xion is to actually thread with her. If we talk things out, there's a good chance it'll stick, but otherwise... poof.
I'm always open to talking over IM or PM, so if we need to work something out plot-wise, just drop me a line. I love IM RP, so if we have to get things done that way, I am totally fine with it.
Best way to summarize this entire thing: When in doubt, ask me! :D