Only The Young: During the initial recording sessions for their ''Raised on Radio" album, the Make A Wish Foundation let Journey know of the plight of Kenny Sykaluk, a young boy in Cleveland dying of cystic fibrosis. Journey flew that day to the boy's bedside, gave him a Walkman with a copy of the then-unreleased "Only The Young" and other memorabilia items. Being at the boy's deathbed greatly affected the band members, to the point that even years later, they still break down in tears recalling it. Full story here, with the Behind The Music retelling here at 5:13.
Arguments can be made for just about the entire game, but the final chapter: after freezing to death on the way to the peak, the White Robes who have been imparting the sad story of their lost civilization restore the player to perfect health and send him/her to the top of the mountain, a Shangri-La-like playground of red-cloth creatures and limitless, scarf-replenishing energy and beautiful, pure snow to slide in, ending in a plateau of sand suitable for writing simple messages or drawing pictures to communicate with your partner.
The Final Confluence. After rising to the top of a great shaft-temple, the Wanderer(s) commune once more with the White Robes as the ceiling lights up in a brilliant display...and illuminate a grand mural portraying the Wanderer(s)'s journey from the empty tombstone-strewn dunes to the mountain. The combination of beautiful imagery and equally-beautiful music positively radiates a very parental pride in the Wanderer's accomplishments.
Hints, however, at Tear Jerker; the mural ends with the Wanderer(s)' beaten down and collapsing in the wind and snow. When the Wanderer looks questioningly at the White Robe, the White Robe's manner is silently apologetic.
For an uninitiated player the list of companion names at the end can be one. If you didn't know before that those were real people accompanying you on your journey, the realisation that you were never going it alone is truly touching.
Not to mention that an uninitiated player, after dying in the blizzard, the player is resurrected alone, and there's no indication that their partner is being resurrected too, and the last, most triumphant part of the journey feels like it must be made alone. Among the most heartwarming moments in the game is finding your partner again.
Any time a partner pauses right at the end of a long journey, so you can walk off into the distance side-by-side.
Players that make an effort to keep their partner's scarfs all charged up, especially when one traveler messes up an obstacle and the other jumps down to help them. It becomes more critical up on the icy mountain, where these two strangers can keep each other from freezing in the snow out of nothing more than compassion. When these two get to the top part of the peak and find that this doesn't work anymore, it usually doesn't stop people from trying.
Relatedly, players that chirp a lot even where there's no need to because the scarves are all charged up, just to chat with their partner. And keep doing so until the end even when you don't have a scarf or even a voice anymore, and you can't hear the sound of your partner's voice or even see the symbol... but you can see their body make the jerky motion as you both trudge up the snowy mountain. Having a partner still tirelessly trying to reach out to you and encourage you even when it has no practical use and you can't hear it... makes the coldest part of the journey the most heartwarming as well.