Every time I think about this RP, my first thought isn't about the potential story or character growth, but rather "Hmm... How can Impmon prank <name> in the funniest way?" XD
Heheh. Getting on Agumon's nerves is all about talking smack to him, and then refusing to give him the fight he wants~ xP But in terms of actual pranking, all there is to that is basically just get him while he's in the middle of training, most likely. Or trying to impress somebody, especially Blucomon~
Hide is a bit of a tougher nut, since he's basically been trained since he was a boy to keep a bit of a professional air about him. But since he's usually serious, forcing him into any kind of embarrassing position or situation would get him. But after the initial prank, he's more likely to just nervously laugh it off with some blushing involved than having any kind of satisfying post-prank reaction xP
As for the exposition vs interaction, while I do think that, ideally, there would be a little bit of confused interaction between the involved parties before the main event actually starts (like what usually happens in a similar situation in various videogames and anime and such), but since we already know what each character's personality is like, such a brief glimpse isn't all that necessary. So for the sake of simplicity and efficiency, it's probably for the best to skip it and get straight to the exposition. xD
