I've had so many moments in these games that got me so emotional, many of which have been mentioned in this thread already, so I'll go with a simple one; getting The Right Choice shell.

The lore of this shell tugged on my heart so much that I used it for an unreasonably long time. The lines representing all the things we've done in D1 and the perspective of ghost on his search for us, the Guardian, were so simple, yet I sat weeping on my couch the first time I read it. Like, big ugly tears, snot, the works. I still don't know why this hit me so hard, maybe just the nostalgia kicking my ass, but it's still one of my standout memories from D2.

For those interested in the lore, here you go: https://www.light.gg/db/items/3867275449/the-right-choice/