
First of all, two questions.
1) Is it alright if he harass your character anonymously, sending them weird messages and stuff?
2) Is it fine if he fourth-walls your character, in the case that he might know about them?
Second, I've filled that meme-like permissions thing
OUT OF CHARACTER
Backtagging: yes, go ahead
Threadjacking/Threadhopping: better ask than be sorry, yeah? sometimes, it might be a thread that's fine to hop, sometimes it might be planned out and not appreciated
Fourthwalling: Yes, it's all alright
ACTION
Fighting: considering how good he is at making enemies. yes, i don't mind, but i won't mind if you plot it out just an outline first
Injuries: considering Mukuro's stabbing Fran all the time, i would feel it a shame to put "no" here, so yes, it's alright, without asking, if it's just light injuries
Killing: that's one i'd have to think case-to-case on, so ask
Telepathy/Mind-reading: actually, it wouldn't be surprising if he noticed if someone is trying, but yes, trying is fine. to make sense of his thoughts, on the other hand
RELATIONS
Hugging: yeah, go ahead. he won't get why, though. but if it's Chrome, he'll get awkward
Flirting: why would you flirt with a kid? but yes, that's fine. if he gets that you're doing it, he'd probably call you names for it
Kissing and/or other intimate actions: as with the two above, he'll just think they're weird and possibly creepy