I'd bring them together in an everyday situation - when they're humans, that is -, probably with a round of friends (like a barbecue, birthday gathering) and then have them try hard to stifle their roused feelings so no one - especially not the other - notices. Have them focus on the "oddball other", and totally ignore their suspecting friends / family.

They'll be acting like complete morons... and have no idea why, and probably misinterpret it, what might lead to more plot-driving shenanigans.

At least, I let my MCs do that. Of course everyone knows, or at least has an idea, why they are acting so moronic. But they need a few (mental!) headbutts by a certain "DAY 12: NONNA STELLA" , a bunch of older sisters and friends to realize - and act on - it.