Heartwarming / Halo 3

• At the start, when they think the Chief's dead or incapacitated, Johnson wants heavy lift equipment, because "We're not leaving him here." And then the Chief's hand grabs him, and he speaks up, and Johnson gets cheerful.
• The Master Chief and the Arbiter start off as enemies briefly, but eventually trust each other after several skirmishes. While the Chief doesn't say more than only one word to the Arbiter, it is clear that he trusts him implicitly, such as when he allowed him to kill Truth on the Ark, and when they became back-to-back against the Flood. They've come a long way since they met in the bowels of Delta Halo.
• In this game, you can come across human soldiers being interrogated by Brutes and being assimilated by the Flood Infection Forms. With some quick thinking and careful shooting, you can save them.
• Cortana the level, when you reach Cortana the person.
  Cortana: You found me. But so much of me is wrong, out of place. You might be too late.
  John-117: "You know me. When I make a promise-"
  Cortana: "You... keep it. I do know how to pick 'em."
  John-117: "Lucky me."
  • As if that wasn't wonderful enough, keeping in mind the background from the Fall of Reach novel makes it even better.
  • Also, this Call-Back right after you've retrieved Cortana, mirroring the start of the first game, delivered in the most heartwarming way by Jen Taylor:
  Cortana: "Just keep your head down... There's two of us in here now, remember."
• Not long after Johnson's death, a piece of ice near the door collapses, revealing a slope for them to climb. Arbiter takes this as a sign that even in death, Johnson is still helping the three heroes find their way home. Indeed as the slop leads them to Johnson's Warthog which they use to drive back to the Dawn.
• After 28 long years, the Human-Covenant War has finally come to an end. On Earth, a memorial is held for the crew of the Forward Unto Dawn, including Miranda Keyes and Avery Johnson.) Following his speech, Lord Hood converses with the Arbiter, and while the former will never forgive the Sangheili for what they did to humanity, he thanked 'Vadam "for standing by him to the end." As they shook hands, Hood expresses sorrow for the apparent death of John-117 but 'Vadam responded with "were it so easy", echoing his first words to Chief at the beginning of the game.
  • The epitaph of the memorial reads "In memory of those fallen in the defense of Earth and her colonies. March 3, 2553" with photographs and other personal belongings to the brave men and women who gave their life defending Earth. As a tribute to the SPARTAN who contributed the most, the number "117" is scratched onto the memorial along with the insignia of the Master Chief ranking tape below it.
• The departure of the Sangheili at the end.
  Rtas 'Vadum: Things look different, without the Prophets' lies clouding my vision. I would like to see our own world. To know that it is safe.
  Arbiter: Fear not. For we have made it so.
  Rtas 'Vadum: (salutes) By your word... Arbiter.
  Arbiter: (a mixture of pride, eagerness, urgency) Take us home.
• Mendicant Bias was a forerunner AI that defected to the flood. He was captured and split in two: One part on the Arc, one in High Charity. What makes this heartwarming? When the Covenant opened the portal, the two parts of Bias reunited. Filled with regret, knowing he was dying, he decided to betray the Flood, and protect John from the dangers of the Arc. Particularly heartwarming is this message to John, found in one of the terminals.
  Mendicant Bias: And so here at the end of my life, I do once again betray a former master. The path ahead is fraught with peril. But I will do all I can to keep it stable - keep you safe. I'm not so foolish to think this will absolve me of my sins. One life hardly balances billions. But I would have my masters know that I have changed. And you shall be my example.
• Despite being stranded in space in the other half of the Forward Unto Dawn that made it through the portal that escaped the Ark successfully, John and Cortana still find comfort in each other, knowing that as long as they're together, they can pull through this eventually with the distress beacon Cortana set up, though Cortana says it might take several years, before anyone picks it up while John undergoes cryosleep.
  John 117: Wake me... when you need me.