Heartwarming: Tales of Symphonia: Dawn of the New World
If you're truly into Emil/Marta, then the scene in Altamira in Chapter 8 is pretty sweet, as Marta truly doesn't want Emil to go at all. Emil really doesn't know what to say, but it does lead to a kiss (though he don't directly see it). It can be a Tear Jerker though when you realize what Emil's planning to do...
Marta's "death" in the Temple of Ice, Emil's sheer and utter fury and then relief as he sees Marta's not dead and hugs her.
Some of Emil and Marta's after battle dialogue.
If Emil finishes the battle with a Mystic Arte and Marta was KOed.
Emil: Are you alright?
Emil: You can depend on me.
Marta: Thanks Emil.
Tenebrae's devotion to Emil when the big reveal happens that he's really Ratatosk. Particularly comforting Emil when he has a My God, What Have I Done? when he realises that Marta was bait.
Zelos' Undying Loyalty towards Lloyd, no matter what Lloyd may appear to say or do. It's good to know that Zelos took Lloyd's trust to heart.