Heartwarming: Assassin's Creed I aka: Assassins Creed
A very big one occurs between Alta´r and Malik, just before Alta´r goes to face The Dragon for the second time. It's especially touching considering the fact that Alta´r is the main reason that Kadar is dead and Malik is crippled. It's arguable that Alta´r's redemption is only truly complete once Malik, who has suffered unimaginable pain because of Alta´r, forgives him.
Alta´r: I've been a fool.
Malik: Normally, I'd make no argument, but what is this? What are you talking about?
Alta´r: All this time, I never told you I was sorry. Too damn proud. You lost your arm because of me, lost Kadar. You had every right to be angry.
Malik: I do not accept your apology.
Alta´r: ...I understand.
Malik: No. You don't. I do not accept your apology because you are not the same man who went with me to Solomon's temple. And so you have nothing to apologize for. ... We are one. As we share the glory of our victories, so too should we share the pain of our defeat. In this way, we grow closer, grow stronger.
When Alta´r is about to succumb to the Brainwashed and CrazyZerg Rush of Assassins, Malik comes out of nowhere with his Merry Band of Four Loyal Guys and a lot of throwing knives to save him. Which is enough to qualify for a CMOH on its own, but then you realize that the reason Malik is in Masyaf at all is because he trusted Alta´r over Al Mualim enough to actually go back to the place where he lost his left arm and his brother died — something that couldn't have been easy.
Alta´r and Malik have another right after Malik's Big Damn Heroes moment. It's an especially heartwarming moment once you remember how Malik greeted Alta´r the first time they met after Solomon's Temple: