Daxter is a heartwarmer in general when you realize that he is the person who has willingly stayed by Jak's side through all of their adventures.
After Damas dies in Jak's arms Daxter pushes aside his usual cowardice to go after Veger in the catacombs.
Jak: You're willing to go down there. Without a fuss this time?
Daxter: Yeah, well, don't get used to it. It's just that nobody hurts my best friend and lives to brag about it!
Jak staying behind at the end of Jak 3.
Jak and Keira's kiss at the end of Jak X and Jak's reaction to it. Even more so because it took four games of almosts to get there.
The interaction between Jak and The Kid during Jak II. The Kid takes a shine to Jak and is one of the few to immediately like the Phlebotinum Rebel. Jak, on the other hand, is visibly startled when The Kid tries to take his hand. And then The Reveal clinches the deal.
Jak: "Stay away from any wumpbee nests on your ninth birthday, okay?"
The Kid: (nods enthusiastically)
The fact that Jak immediately reverts back to normal upon recognizing Daxter. That Daxter can ride Jak's shoulder safely even while Jak is going berserk. Daxter matching his pose to Jak's mood during those moments.