General Permissions
[OOC]
Backtagging: Yes, please. ♥ Also, never hesitate to nudge me!
Threadhopping: In most cases, it would be okay, where appropriate. Unless it's something intense or important, but ask if you're not sure.
Fourthwalling: In the sense of him being a video game character, then no, considering his role in canon. I am fan of dramatic irony, however, and jokes or references that go over his head are fine. If your character happens to know Sephiroth from another game, like Kingdom Hearts or Dissidia, then definitely feel free to recognize him.
[IC]
Hugging this character: Yes! Sephiroth needs hugs. I don't know how it'll go, but he could use some.
Kissing this character: Why not? Attempt away. How he responds will very much depend on her relationship with the other character, but a cold rebuff is probably the worst they'll get.
Flirting with this character: Yes. It could be hilarious.
Fighting with this character: Fighting with Sephiroth is of course welcome. Under normal circumstances, he's unlikely to start a hostile fight without good reason. Sparring's another matter, and he's always happy to find a new opponent to train with.
Injuring this character: Ask first. Sephiroth is notably hard to injure in his canon, but I'm not completely opposed.
Killing this character: If there's a good reason or story behind it, then maybe yes, but we'd have to work that out beforehand.
Using telepathy/mind reading abilities on this character: Yes, although he would probably be difficult to read. One might be able to sense that Sephiroth isn't entirely human or that there's something alien about his brain. If you tell him this, though, he's unlikely to believe you without proof.