This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Arashi no Yoru ni
When both Mei and Gabu have to leave their families and homes to be together.
The beginning, when Mei's mom dies protecting him as a baby..
As they are fleeing their homeland, Mei and Gabu have a variety of dangerous encounters that has them fearing that the other is dying or dead. Then when Mei offers himself to be eaten by Gabu so he won't starve, Gabu will have none of it and has an emotional breakdown. At the end when Mei and Gabu are reunited, Mei is horrified that Gabu doesn't remember him and wants to eat him, but Mei will only be eaten at all by the Gabu who is his friend. Gabu regains his memory and they are happily properly reunited to live out their lives together.
Gabu's emotional meltdown in the snow cave. "Why was I born a WOLF?"
The unofficial English dub has the line as, "Why did we have to be born the WAY WE ARE!?" Either way, it's pretty heartwrenching.
The scene where Gabu is sitting alone in the well and then has a flashback about when he was teased as a pup for being too scared to make the jump. The scene itself added nothing to the plot, but it was depressing. Because, it established that Gabu was always seen as the odd one out in the pack, and that he probably likes to spend some time alone and away from the pack.
it also cements how painful the idea of Mei just using him for information on the wolves is, which is what the others have tried to convince him of. He's always been made fun of and left out, and now that he finally has a friend who he trusts, he's forced to question whether that friendship is even real...
The Happy Ending of the film quickly makes a turn for this if you choose to believe in the theory that Mei and Gabu died on the mountain and the ending was really them reuniting in heaven.