The end of "Haunted". Elena asks Stefan to erase Jeremy's memory of Vicki being a vampire and dying, but Stefan tells her he isn't powerful enough to do it. Just then, Damon shows up and tells Elena he'll do it, if that's what she wants.
In "Fool Me Once", Anna's utter joy of being reunited with her mother.
Damon's completely honest concern regarding Elena's safety and his determination to rescue Stefan in "Let The Right One In" is this.
Damon dancing with Elena in "Miss Mystic Falls" covering for his brother who was too busy running off into the woods and trying to kill people.
Isobel's I Want My Beloved to Be Happy moment at the end of "Isobel", when she compels Alaric to stop mourning for her and instead to move on. While not erasing the hurt that he felt over her becoming a vampire and leaving him, it clearly takes the bitterness out of him and gives him peace of mind (or as much as there can be in a show like this.) Considering that she had been portrayed as The Sociopath for most of the episode, it was one of the most heartwarming examples of Mood Whiplash this troper has seen in a while.
The bathroom scene in 2x02 between Stefan and Caroline.
Stefan: I promise I will not let anything happen to you. Come here. *he hugs her*
The last scene between Elena and Caroline in "Kill or Be Killed". Especially the way Elena hugs Caroline to confort her. Aww.
Stefan apologizing to Damon at the end of "Rose" and telling him that he only turned him because he didn't want to be alone. "I guess I just needed my brother."
Bonnie and Elena comforting Caroline after she was captured and tortured by werewolves under the song "Losing Your Memory" in "Daddy Issues".
Stefan with Caroline earlier in that episode.
"You don't have to pretend with me."
Tyler's mother completely accepting him after learning that he's a werewolf, and promising to save Caroline, who she just found out is a vampire.
Kind of an odd one given all the horrible things they did, but it's kind of sweet when Klaus reveals the real reason he wanted Stephan with him was because of how much he treasured their friendship.
Watching a bunch of vampires bond over murder and booze in the 1920s and come back together has never been so oddly heartwarming.
Damon promising he is never going to leave Elena again and the obvious guilt he is feeling at leaving in the first place in 3x05.
From "Ghost World", both Grams telling Bonnie she is proud of her and Anna reuniting with her mother.
The simple facial expressions alone cemented the reunion of Anna with Pearl as possibly one of the most heartwarming things this troper has ever seen.
"Ordinary People"is full of this, most specifically Elena telling Damon that he's going to be the one to save Stefan.
"It won't be because he loves me. It'll be because he loves you."
From the same episode, Damon and Stefan's brotherly bonding, right from Damon busting Stefan out of his prison to Stefan betraying Klaus when Mikael threatens Damon to Damon telling Stefan why he has to save him.
Also, all the flashbacks of the Original family, especially Klaus, Elijah and Rebekah standing over their mother's grave and swearing to stand by each other, "always and forever".
Matt giving Rebekah a ride home. At first, she thinks it's because of a romantic interest or some manipulation on Caroline's part, causing Matt to reply that "Its sad that you can't get a ride home without thinking there's an ulterior motive". Then you realize that Matt is probably the only person in about a thousand years of existence who has shown her genuine kindness and affection without wanting anything in return. Rebekah's smile pretty much seals it.
Klaus surprisingly gentle and kind Pet the Dog moment with Caroline, encouraging her to keep living and see everything life has to offer especially an immortal life, and genuinely seeming sorry about hurting her. Telling her he loves birthdays and getting her a birthday present pretty much seals the confusingly heartwarming encounter. Time will tell if it's genuine, the start of some sort of romance, or him just being a Manipulative Bastard.
Any scene with Klaus and Caroline is heartwarming, creepy - considering the fact that he pretty much order her death at one point, but heartwarming all the same.
It's probably just me, but the scene where Caroline and Rebekah are talking in the beginning of Before Sunset seemed a bit heartwarming.
Caroline's genuine joy as she agrees to run away with Tyler to escape the Council.
Damon not joining Stefan to fight in World War II, because being around him might cause Stefan to relapse into The Ripper again. Also heartbreaking, because this is one of the few flashbacks we see where Damon is actually glad to see his little brother, and does the unselfish thing for him. Stefan wouldn't know about it until many years later.
Stefan taking Rebekah to the (now cancelled) eighties-themed school dance. We get a glimpse of the kind of girl Rebekah was/is when she's not an Original: sweet, somewhat awkward, a bit snarky, even shy at times.
And from the same episode, Stefan refusing to dagger her when she lets her guard down and tells him why she wants the vampire cure: so she can have the life that was denied to her when her parents turned her and her siblings. It's possibly the first time in the whole series that Rebekah hasn't been literally stabbed in the back.
Caroline, while dying from Klaus' werewolf bite, tells Klaus that she knows he's not pure evil, and acts the way he does because of the hurt he has inside, and that there's a part of him that's still human. Klaus asks her how she can possibly think that. And Caroline's response?
Caroline: Because I know that you're in love with me. And anyone who is capable of love, is capable of being saved. But I guess I'll never know...
The expression on Klaus' face says it all. And he does end up saving her life with his blood. And while there's the possibility that Caroline is just saying this to save her life, Klaus' reaction is the most genuine thing he's ever expressed that isn't psychotic rage.
Caroline and Klaus again in episode 4x18. She's trying to help him remove the white oak stake that Silas snapped off in his body...only for both of them to find out that the stake and Klaus' pain were just hallucinations sent by Silas. Klaus gives Caroline the most heartfelt thanks he's ever given to anyone and sorta-kinda hints that he's going to leave Tyler alone. Caroline's departing smile at him is sweetness personified. Klaus' own smile will make you want to vomit rainbows.
Elijah revealing that he's complete aware of the kind of person Katherine is in 4x18, and that their renewed relationship might be one of convenience on her part...but he still hasn't given up on her and still loves the girl she used to be, saying that "...My Katerina must be somewhere underneath that Katherine facade."
And from the same episode, Katherine gives Elijah the vampirism cure, saying that he's the only person she knows that will still stick his neck out for her. The cure is the only thing that will ever keep her safe from Klaus forever, and she gives it to Elijah - knowing that he puts family above all else - to show that she does trust him, and possibly loves him as well. Even better, she leaves their relationship entirely in his hands, with no manipulation from her end.
Klaus' obvious happiness as soon as he hears Elijah's voice on the phone and the fact that his brother is coming back home, albeit with the Cure and some demands.
Tyler coming back to see Caroline for their senior prom.
Klaus' Pet the Dog moment from the same episode, when he allows Tyler to get out of town alive, all for Caroline's sake.
Rebekah offering to use her powers to not only get Matt to graduate, but to get him a full scholarship into any school he wants. And when he rejects it, she decides to tutor him instead.
Know what else makes this moment sweet? It's obvious that she waited for him to revive from Jeremy's ring after Damon snapped his neck. For however long it took, Rebekah sat there and waited for Matt, the closest thing she's had to a genuine friend all series, to come back.
Really, just Rebekah in this episode. It's the only episode we see her be genuinely remorseful about how she's acted to the cast (Matt in particular), and trying to help and make amends any way that she can. The only time we've seen Rebekah be this nice was over a thousand years ago, when she was still human.
Elena finally turning her humanity back on in 4x21. It took Matt dying violently in front of her to do it, but it proved that Emotionless!Elena had some love still buried inside her.
A subverted one from 4x21. As Stefan helps Elena from letting her emotions overwhelm her, he tells her to focus on the one thing that makes her strong. From the way she looks at him (and from Damon's briefly heartbroken expression) and the music that swells, it's implied that she's focusing on her love for him to bring her back. But it turns out that was pure, unadulterated hatred for Katherine Pierce.
When Bonnie lifts the veil, and nearly every main character gets a chance to talk to their loved ones again. Special note to Damon's pure and unbridled joy when he sees Alaric again.
Only topped off by Elena and Jeremy seeing each other again.
Elena sharing a lunch with Alaric and Jeremy. It's the happiest she's been in a long time.
Klaus telling Caroline that Tyler is free from his vengeance. When she asks him why, he says "He's your first love. I intend to be your last...however long it takes."
The expression on Damon's face when Elena tells him that she's in love with him.
"I got the girl." Made all the more heartwarming by the presence of his best friend as he realizes this.
And speaking of which, can we just put any and all moments between Damon and Alaric in the season 4 finale into this category?
Just as Stefan is about to give up and turn his humanity off, a vision of Elena appears to him and she begs him to keep his humanity for her. Keep in mind that Stefan is currently entombed at the bottom of a lake and has been constantly drowning for three months, it's not only a testament to his will, but also his love for Elena.
Damon's Screw Destiny speech after Qetsiyah tells him that the doppelgangers of Amara and Silas will always end up together no matter what.
Bonnie using Jeremy to tell her friends how much she loves and misses them, and how she wants them to live their lives. This happens during her memorial, and seeing all her friends (even Damon!) smile even while they grieve...
Tyler comes back to Mystic Falls for Bonnie's funeral.
Nadia revealing to Katherine that she's Nadia Petrova...aka Katherine's infant daughter that she was forced to give up due to the shame of having birth out of wedlock. Taken further when Katherine reveals that she went back to Bulgaria and searched every village and every town for her little girl, but couldn't find her.
Silas' reaction when he sees that the Anchor for the other side is none other than the fossilized body of Amara. He immediately feeds her, abandons his plans and looks ready to carry her out of the warehouse and just go. Silas has spent every moment since his introduction going on about his 'one true love' and the lengths he'll go through to die and be with her. In those few minutes, we can see that it wasn't talk at all.
Bonnie coming back to life so she can serve as the new anchor to the other side after Amara's death. She goes to say goodbye to Jeremy, and suddenly he can feel her. Then Elena and Caroline come inside and they can see her. Cue happy hugs and tears.
In 4x15, Damon's response to finding Bonnie is "I could actually hug you right now." And then he does.
The end of 5x14, which is dedicated to recently-deceased crew member Sarah Jones.
Katherine giving a dying Nadia a hallucination of what her life should have been like: happy, carefree and living with her mother in a simple cottage.