DC Universe Original Animated Movies/Heartwarming

Batman: Under The Red Hood

The final scene, where a flashback occurs showing Jason's first moments after putting on the Robin suit. Doubles as a Tear Jerker when taking into consideration the Foregone Conclusion.

Jason: This is the best day of my life!

Ra's Al Ghul saying "I've done enough" as Batman leaves. Considering this is Al Ghul we're talking about, this is actually rather touching.

Is it any surprise that a movie dedicated to Superman and Batman's Bromance would crop up a few of these? An understated but no less touching example is when Superman decides to meet with President Luthor despite it's clearly being a trap. Batman dourly tells him that he shouldn't expect Batman to save him. After Superman walks into Luthor's trap and is attacked by Metallo, Batman of course shows up in the nick of time to rescue him.
In the climax, thanks to Luthor's interference, Batman enters the rocket to manually control it in a suicide mission to take out the Kryptonite meteor. Superman furiously tells Luthor, "That's my best friend you just killed!"

The Wonder Woman animated movie had a particulary endearing one. Artemis spends most of the movie criticizing Alexa for focusing more on reading than on battle training. Alexa eventually dies, and after a sad goodbye with a ghost Alexa, Artemis is seen by the end of the movie with a pile of books besides her.

Hyppolita: Are you reading, dear sister?
Artemis: I am trying, my queen, but it is fiercely boring.