Ben 10: Alien Force/Heartwarming

Pretty much anytime Reinrasic III and Ben interact, knowing how much the latter has caused the former's character to develop from a racist supremicist to one of Ben's closer friends and staunchest allies. Added "D'awwww" points for Reinny's unintentional pet name for Ben: "BenbenTennyson."
Kevin embracing Gwen after she frees him from the Nightmare Fuel of a transformation into kadanite.
Gwen assuring Ben that she knows Julie would be thrilled to go out with him.
Gwen holding Ben in her arms when he nearly passes out in "Darkstar Rising."
Ben in "Alone Together." Pretty much everything he did.
The entire ending of "Voided." Period.
The last five minutes of Paradox.
In Ultimate Alien, Charmcaster's Heel Face Turn and friendship with Gwen in "Where the Magic Happens". Especially when she tells the guy who wiped out her magic-using species that "you can't get rid of all of us", referring to her people. And as she says this, she smiles at Gwen and holds her hand, showing that she's accepted her one-time enemy as basically a sort of sister.
Again in Ben 10: Ultimate Alien. In a sick, sad sort of way, Kevin's "Can I have Quarrel back?" in Nor Iron Bars In a Cage to the prison warden was kind of heartwarming. The interaction in the flashback between Quarrel and a newly human-looking Kevin was also incredibly cute.