Looking back, the Thunderbolts' first hero team-up with Spider-Man is this for Mach-I/the Beetle/Abner in particular. He has some past history as an adversary of Spider-Man, and was initially all in favour of the idea that he now has a justified reason to go after the wall-crawler, but after Spider-Man helps him fight off the brainwashed Thunderbolts, while Jenkins justifies his decision to let Spider-Man go as Pragmatic Villainy, he admits later that when he made the initial suggestion, he was just thinking about how it was the right thing to do, marking the first sign of the Thunderbolts Becoming the Mask.
The Thunderbolts taking Jolt on the team, giving her a new home and family. Granted, Zemo and Moonstone did it out of Pragmatic Villainy, but the others genuinely cared about her, and this was one of the early signs they were really starting to change for the better.
Moonstone helping Jolt get over the trauma from her backstory that resulted in her hating school.
Or as heartwarming as a bunch of super-villains can be. Learning that they actually do give a damn about each other, despite their attitudes towards each other, in order to give an epic Curb-Stomp Battle to Hyperion that doubles as a Moment of Awesome.
The insanely paranoid Ghost opening up to Moonstone JUST enough to share his origin with her. He even ponders if this is supposed to be a heartwarming sign of trust or simply a sign that he no longer views her as a threat.
The time-travelling Bolts sharing breakfast in #169. It's a charming little moment, a routine, everyday thing from this group of misfits and outcasts in the midst of the weirdness they're going through.
In issue #181, Troll is put in the position for the first time of actually having to take a human life in order to help the team as they lead a mutant army against a army of Judge Dredd inspired future police with tears in her eyes. Before she can swing her axe to kill one that was attacking Boomerang, Mr. Hyde grabs her and flings her to the group's destination where there would be no enemies and takes them on himself.
