The story of Joe, a Ewing's Sarcoma patient who was invited to tour Riot through the Make-a-Wish Foundation. Riot then put Joe's favorite skin, Jaximus, on sale, with all proceeds going to Make-a-Wish. When Joe passed away, Jaximus got a unique new line. "Here's to you, kid!"
Riot artist IronStylus was tasked with designing a female tank champion. He needed a strong woman to base her on... so he asked his wife to be the model. He later admitted Leona's default art is more or less an unaltered portrait of his wife, just with her hair and eyes colored orange.
Trials of the Poro, a short movie about one of the game's mascot Ridiculously Cute Critters getting caught up in a huge battle somewhere in Freljord while searching for Poro Snax. The heartwarming comes in when the terrified little poro is saved from an enormous Rain of Arrows by a huge, cheerful, bald warrior with a giant shield and a Badass Mustache (actually the first reveal of upcoming champion Braum) who, after saving him, arranges his fur into a little mustache of his own.
Braum: Next time, you get my back, eh?
Braum himself is essentially a Crowning Character of Heartwarming in many ways. Not only is he a Spirited Competitor and ultimately friendly to every other Champion in the league, but this carries over into gameplay as well - his entire kit is dedicated to protecting his teammates and shielding them from enemy attacks. You will feel good playing this Champion or being supported by him. His W skill, titled "Stand Behind Me," is often accompanied by lines such as "Stand behind Braum!" or "And you thought you were in trouble." His whole personality can be summed up in one of his movement quotes:
Braum: "Sometimes icy heart just needs warm smile."
Compounding this is his backstory/lore. What was that, you thought he'd be a Stepford Smiler with a tragic backstory to make him look like a Sad Clown? Well, NOPE. Braum's lore is basically just yet another his folk tales about saving other people. He's always a positive Nice Guy from get-go and has always been as such from start to finish. There's no such thing as angst in Braum, he's genuinely friendly, cheery, supportive. Sometimes, in the world where 'edgy is cool' and True Art Is Angsty, it's always assuring that there are guys like Braum, like saying that you don't have to be dark and edgy to be cool, and being a Nice Guy isn't that boring, but awesome.
Reginald: Fear of Failure features Team Solomid's captain Andy "Reginald" Dinh and his tale of going from a troubled schoolkid to the leader of one of America's biggest teams. It's really inspiring and almost goes into Tear Jerker in a few parts.
"There's always gonna be that bad guy, and I don't mind being it."
Who says that even fandom can't make a heartwarming story, even if it's probably non-canon? Take a look at She Who Is Like A Sun To Me, which takes Pantheon's baker joke and Leona's protective instinct into a story of sweet friendship that may shed a lot more humanity on the war-worshipping Rakkor warrior, and launch the Pantheon/Leona ship even further. note The summary: Pantheon used to be a ostracized Rakkor kid because of his baking hobby, with everyone else bullying him for that, and only Leona staying as his friend, driving away the bullies and enjoying his cakes. Even as he became the paragon of Rakkor and their way of warrior, and Leona became a member of the Solari, Pantheon will always see her in high regard.
And if you look at the comments of the link... it looks like IronStylus loves this one.
Well speaking of Blitzcrank/Orianna, you may want to check out this short story Deus Ex Machina which involves some Tear Jerker, some Moment Of Awesome, but most importantly, lots of feels for the two. Guest starring Viktor.