Cleos is, frankly, not super impressed with the latest batch of heroes sent to stop her. What, some gangly bird lady cleo could snap like a twig and a fairy with plant powers of all things? against the one who's able to rot anything she touches?
They're kinda cute though, and she's feeling generous to the ones sent on a suicide mission, so she lets the bird girl get in one free hit. Next thing she knows she's sitting in the ruins of what was once a solid concrete wall getting tied down by vines thicker than her arms.
She'd be lying if she said it wasn't the hottest thing that'd happened to her in months. She still escaped, obviously, but found herself hoping to see the two again sometime soon.
And see them again she did. They started to clash fairly regularly after that, constantly finding new ways to combat each other and maaayyybe flirting a little bit as they fought (though if you were to ask any of the three, they'd vehemently deny having any feelings for the enemy, just responding that flustering the opponent makes better opportunities. if you know what's good for you you'll ignore that they get just as flustered when it's sent back at them)
Eventually, as heroes do, the other two get in over their heads (Cleo had learnt their names to be Symmetry and Monster by now). They took on a foe too strong for them, and were severely injured. They knew that they couldn't get to a hospital in time, and there were only really two options: bleed out in an alleyway or try their luck at the hideout they knew Zombie had nearby.
(and maybe, if in the ensuing conversations some things like feelings and names happen to accidentally spill out then. well, Cleo had been growing somewhat tired of the villain life for a while anyway even before those two showed up, and honestly? she's willing to give a side change a shot for them (later, stress and false will both tease her relentlessly about how she got power of love'd into switching sides but she doesn't see them complaining when she's kissing them so ha)
(all three of them fail to notice the copious amounts of money that change hands amongst both hero and villain circles (and some even between heroes and villains) once they go public with their relationship)
Cleo's certainly still no hero, and she's been quite firm with her girlfriends that she never will be. She's spent too long in the villain lifestyle to deal with all those rules and expectations. She beats to her own drum, not whatever some government determine is 'acceptable'.
But, she'll play nice for her girlfriends.
False is a lot more realistic of a hero. She knows what's achievable, and she's careful with what risks she takes. Stress is more idealistic, even if she's happy to get her hands dirty occasionally. They balance each other out on the field, and Cleo fits perfectly into that dynamic.
Working together seamlessly is built on a foundation of trust, after all. And man, is that something they're great at doing behind closed doors.