I‘ve never heard the term rarepair, so I’m just assuming that you mean not commonly talked about pairings.
Now, you might’ve already read on the lovely @skzms blog that I kinda ship them all with each other, so really every pairing is encompassed here. My main pairings in no particular order are Minsung, Hyunlix, Changseung and Chanin, which aren’t really uncommon, I think.
So for rarer pairings, I think Hyunseung would be nice (they’re not nice, they’re pure chaos, never leave them alone or the whole house will turn into ash) in this pairing, I just imagine Hyunjin to be a huge brat, always teasing and testing Seungmin, who joyfully always puts him back in his place - until one day he doesn’t. Hyunjin keeps on playing, pushing him around, taking what he wants without asking, expecting Seungmin to at some point break and get back at him, but instead he just takes it, lets himself get taken, and it’s an absolute thrillride for the both of them. Hyunjin can’t believe his luck to finally have his partner in all the ways he never could before, and Seungmin just lets himself drop and enjoys the attention. Their relationship is never the same since, as a whole new power dynamic has been introduced, and the constant push and pull is endlessly entertaining for them (albeit sometimes a bit annoying for the other members, who tell them to just get a room already)
Also I want to mention that while I already talked about Hyunsung, I don’t think anyone expected that. Yeah, sure, they were playing around a lot beforehand, but that’s exactly all it ever was in the eyes of everyone (including themselves): just two guys playing around being funny. Once it actually escalates, everyone‘s stunned that this is actually happening.
I hope this answered your question, but feel free to drop into my inbox anytime to elaborate :)