The second mission of the campaign has Raynor and Kerrigan teaming up to fight their way out of the Umojan facility as it's being attacked by the Dominion. "Reminds me of the old days".
The cinematic before the mission also counts, with Kerrigan kissing Raynor on the lips.
When Kerrigan hears about Raynor's apparent death, a lone zergling walks up to her as she's crying as if its trying to comfort its former master. Its kinda heartwarming in a girl and her horrific man-eating monster sort of way.
Kerrigan grooming Zagara both genetically and as The Mentor to understand how to lead the Swarm as she does. Even if she dies pursuing her vengeance, the Zerg will endure and have a leader able to combat Amon when the time comes.
At the end of the Char arc, Kerrigan letting escape ships full of injured men go free. The is doubly impressive for any long time fan of the series. She did the exact opposite at the end of Brood War against the UED; no one who played the original game would have expected such a selfless display of character. Her actions really proved that she was NOT the same "Queen Bitch of the Universe" from before.
Remember in the first trailer for Heart of the Swarm, where you hear a terrified Marine scream, "There's too many Zerg! We're not going to make it!" ? He was wrong.
Marine: General, the Zerg pulled back! It's a miracle!
Kerrigan's interaction with Stukov toward the end of the Skeigar missions. After both of them team up to defeat Narud, Stukov expects Kerrigan to eliminate him, and honestly doesn't mind, since being now half-zerg half-human, he has nowhere to go anyway. Not only does Kerrigan spare him, but, feeling Not So Different with him, she offers him a place in the Swarm. He accepts.
Stukov reminisces about his past while in orbit above Korhal.
Looking down on this planet reminds me of a dear friend. Gerard, may you rest in peace.
When the Raiders get involved again, it's because Kerrigan has learned that Raynor is still alive, and needs their help finding out where he's being held. Horner (and by extension the Raiders) jumps at the chance. Forget that Kerrigan's a Zerg again. Forget that she shows up stronger than ever in a Leviathan, even though the Swarm had been broken at the end of Wings of Liberty. She's brought news that the boss isn't dead, and that's good enough for Matt.
Though it's just a throwaway line, the following cut scene shows that Tosh was willing to break into the prison ship and free Raynor himself, even though it made the previous prison he'd broken into look like a cakewalk. He sure wasn't kidding when he was referring to Raynor as his "Brother".
The ending mission. While you're preparing to fight, inch by inch, towards Mengsk's palace. Guess who shows up? It's goddamn James Raynor and The Hyperion. Kerrigan may be Zerg, there may be no hope of the two of them ever retiring happily, but he'll be damned if he doesn't do his damned best to help overthrow Mengsk. What makes it extra heartwarming is the conversation as he makes his entrance - remember, last time they talked, he was chewing her out for having thrown everything he worked for away just to get revenge, even going as far as to recount the billions of people she's killed, not to mention Fenix.
Kerrigan: I sense... no.. it can't be..
Izsha: My Queen, a terran battlecruiser is inbound on your location.
James Raynor:We're both tied up in whatever happens here today. We do this together.
Kerrigan: Jim... Thank you.
James Raynor:Thank me later, time to put your warface on!
And damn if he doesn't pull through. Without him the ending would've looked a whole lot bleaker. Three words marks his Big Damn Heroes entrance:
Change of plans!
What gives the ending scene its strength is that, when At the brink of death by Xel'Naga artifact, what saved Kerrigan was not her innumerable Zerg swarm nor her god-like powers. It was her honest change for good that convinced Raynor to help her out.
Also, that "Thank me later"? Turns out that she DID say "thank you" again. As for his entrance, he HAS scores to settle with the Emperor. Raynor may have shot Tychus, but he didn't forget who put Tychus in that suit.
During the final battle, when Mengsk sends The Odin after Raynor, Raynor is prepared to sacrifice himself if it means Kerrigan will defeat Arturus, telling her to go on without him. Kerrigan's reply?
"Like hell I will! Hold on Jim I'm coming."
It's extra heartwarming when one considers what happened last time Jim told Sarah to go on without him. She was NOT going to do a repeat of that one.
Honestly just watching the on the battlefield interactions between Kerrigan and Jim's respective armies is kind of heart warming. The attack forces that Raynor sends out are sort of small but they can have huge impacts if the Dominon is too busy shooting at your zerg to keep them from stopping Jim's siege tanks from deploying wherever he wishes. Also while Ultralisks are incredibly durable they also have super slow hit point recovery, unless a Medivac floating above keeping them in tip top shape, then they're even more unstoppable than normal! Never before have enemy crushing unit combinations been so heartwarming...
This is only the third time in the entire series that two armies of different races fought alongside one anothernote If you don't count the Enemy Mine against the Queen Bitch of the universe during the climax of Broof War, and it mirrors both of the previous instances — the UED using its troops and "slave broods" against Kerrigan in Brood War, and Raynor and Tassadar fighting together against the Overmind. After being on the losing end of combined-arms fights at least twice, it's nice to see her on the giving end for once.
Also, Raynor in the ending cinematic. After everything that's happened in the expansion (being captured by the Dominion, finding out that Kerrigan willingly turned herself back into a Zerg after being deinfested), one might not blame him for crawling back into a bottle and leaving Horner to do all the heavy lifting again. Instead, it actually looks like he's going to be okay. Finding out Kerrigan is now less the Queen Bitch of the Universe, and more just Sarah-as-Zerg must have helped some. Even if it didn't end up quite like he thought it would, Wings of Liberty wasn't wasted effort. Hey ho character development.
"My pleasure, darlin'. Always was." Cue Jim's heartwarming smile.
After betraying and/or murdering every sympathetic character during Brood War, and getting away with it scot free, Kerrigan had become one of the most reviled characters in video game history. Taking the necessary actions to redeem herself was something no one expected of her, but not only is her character development believable, it's also what saved her life in the very end. It's a rare and wonderful thing for such an iconic villain to become a hero.
Increasing the Irony is the fact that in both Heart of the Swarm and Brood War, the ending cutscene is called "Ascension"; in Brood War it symbolized Kerrigan as the monster that she had become, in Heart of the Swarm it symbolizes the hero she has become.