I think you could get away with no plot, just them meeting every now and then, *hints* of something happening on the outside, them talking about stuff.

Like, work, work, Kitten on some rooftop and weird conversation and maybe flirting, work, weird it dude, work, passionate discussion on the subject of appropriate costumes for superheroes on some alley with Kitten, work, work, definitely flirting with Kitten after fixing a bank robbery situation, weird it dude at work, work, work, Kitten something, work, newspapers making a huge deal out of the 'secret affair', work, more work, It dude, sex with Kitten, more sex with Kitten...
Something. You know what I mean.