At the funeral of Deckard Cain, Leah bitterly brushes off the attempts of Tyrael at comforting her, rebuking "What would you know about sacrifice?" He took her hand and showed her through his eyes how he was willing to defy Imperius, and hence Heaven Itself, to give up his status as an angel to protect the humanity he so loved. Leah was so moved by this gesture of love and kindness that she shed Tender Tears at the revelation.
This exchange between Lyndon the scoundrel and the barbarian:
Scoundrel: "If I keep helping you kill the lords of Hell maybe I'll be a good person, eh?"
Scoundrel: "Are you serious?"
Barbarian: "You already are one."
Another exchange involving the scoundrel, with the Witch Doctor:
Scoundrel: "What would you do without me?"
Witch Doctor: "Miss your company!"
Counts as a Call Back since there is an Act 1 exchange in which Lyndon muses what the Player would do without him. The response being "Enjoy the quiet."
This little exchange shows that in spite of finding the Monk to be stuffy and far too serious, Lyndon the Scoundrel really cares for the Monk as a friend:
Lyndon the Scoundrel: You look so grim, isn't this your noble quest?
Monk: I do what I must, why?
Lyndon the Scoundrel: Well... you worry me at times.
In Act III there is a an older soldier and his wife who have several heartwarming conversations. In one she congratulates him for throwing the demons back.
Soldier: "You know, there were other soldiers out there besides me, in case you didn't notice."
Wife: "No, I didn't."
Made all the more heartwarming by their previous interactions as an old married couple, with all the bickering and stinging that that implies. Then Diablo goes and kills the both of them, and you find the wife's burial wishes, where she very calmly states that they're both dead, and want to be buried together, but without the soldier's sword, because "he won't be needing it anymore".
Random dialogue with the Templar as a Demon Hunter elicits a mention.
Templar: "Your valor places you amongst the highest ranks in my order."
Demon Hunter: "Thank you. But I am more proud to call you my friend."
Templar: "As am I."
Gets even better when you remember back in Act I, when the Demon Hunter really did not like the idea of having company.
The following conversation with Lyndon the Scoundrel near the end of the game, which is a major Pet the Dog moment for the player character:
Player: I have a gift for you, Lyndon.
Lyndon: Is that so?
Player: Take this gold. When this is all over I will go with you to Kingsport. There you can pay your debts and your brother will be free.
Lyndon:*Genuinely touched* You are much too kind.
Player: We have journeyed together a long way. I am happy to help you.
Lyndon: Words fail me.
Player: Words are not always needed.
Monk: I bear a gift for you, Lyndon. Lyndon: Is that so? Monk: It is enough gold to let you make amends with the Merchants Guild and free your brother. I will accompany you to Kingsport when my duties are met. Lyndon: I do not deserve this. Monk: You have helped me do the will of the gods. You deserve nothing less than peace. Lyndon:*genuinely touched* You... really are a holy (wo)man, aren't you? Monk:*chuckle* So they say.
Kormac the Templar during the final stages of the game is a much humbler man than he is when he first joins the player character, openly admitting that he misjudged both Lyndon and the PC and apologizing to both for his arrogance. Aww.
Mayor Holus' little Character Arc: When we first meet Mayor Holus of New Tristram, he is stuck in the middle of town, because his cart broke and blocked the street as he was trying to flee. The Nephalem has little respect for a coward who would abandon his town in its hour of need. Then we meet him again at Bastion's Keep, and he has not changed a bit, still thinking to flee the fortress before the fighting begins. The Nephalem, fed up, gives him a piece of their mind, to which Holus replies that he simply wants to live. Later, as the demon attacks wane, Holus has his chance to run, but wonders if it wouldn't be better to fight for his life instead of running forever. Surprisingly, he keeps to his word and stick around, eventually dying in the final struggle at Bastion's Keep. A nearby guard says that he never did run, even though he had the chance to at one point.
There is a mini plot arc in Act II of an exiled noblewoman and an Iron Wolf swordsman. She starts off as a Rich Bitch with bits of Fallen Princess, while he is a Deadpan Snarker to her. He helps her survive her exile despite his distaste for nobles and she becomes a Defrosting Ice Queen. He saves her during the Harrowing of Caldeum and the two become an official couple.
Likewise, Kala's little character arc in Act II. She's a former noblewoman who was thrown out of the palace when Belial took over. Having never set foot outside the palace, her first days in the Hidden Camp are quite terrifying for her, though she's inspired by her newfound freedom. Her little character arc ends with her ditching her extravagant clothes and make-up and starting a new life on the road as an ordinary traveler.
Kala: Caldeum was never home to me. It was a beautiful prison. I may die out there on the road, but it will be in the open air, with the world stretching out before me.
Your final conversations with Leah in the Armory as she is trying her hardest to keep the Black Soulstone together with all Hell trying to get in. Turns into a major Tear Jerker later though when Adria's betrayal goes down.
Freeing Auriel from Rakanoth in Act IV not only restores hope to the angels of the High Heavens, but also to the people of Bastion's Keep, who had been hit with major despair following Adria's betrayal and Leah's death.
Going through Act IV with Lyndon, your character points out his gold gathering has become rather lax. He basically replies "Screw the gold, this is for Leah." For all his debauchery and shameless come ons, he genuinely cares about her.
Barbarian: You missed a coin back there, Lyndon.
Lyndon: What of it? It's not about the gold anymore. This... this is for Leah.
To the point that if he ever has a daughter, he's naming her after her.
One Lyndon's Closing Dialogue after you defeat Diablo:
One of the idle exchanges between Kormac and Lyndon around Act III, IV, or Adventure Mode:
Lyndon: I have watched you for some time now, and I would have you know that I am impressed.
Kormac: Well, you've slain a fair number of foes yourself.
Lyndon: Your prowess is undeniable, but I meant you are a strong man who fights for what is right.
Kormac: That is odd, coming from a criminal.
Lyndon: I can be wrong on the details—like who owns this jewel or that coin. It does not mean I am wrong when it counts.
In Reaper of Souls, Kormac's awkward attempts to confess his feelings to Eirena (also doubles as a Crowning Moment of Funny). Keep in mind that in the regular Diablo III campaign, the player character flat-out told Eirena that Kormac was in love with her. So she knows, but Kormac doesn't know that she knows. It plays out like a teenage boy trying to work up the courage to ask out a girl that he likes.
Eirena: I am glad we were able to talk, Kormac. I feel like I know you better now.
Kormac: I would like to know you even better, Eirena.
Eirena: Uh, what does that mean?
Kormac: I, uh... I don't know.
Eirena: Oh! Well, then. Yes?
Also from Reaper of Souls, you have the chance to help Covetus Shen finally track down the Jewel of Dirgest, and learn more about the legend behind it. At the very end, when speaking to the ghost of the woman who may in fact be his true love, Shen becomes much more solemn and sincere, and gives a rather heartwarming remark:
Liria: Whoever you are, you have freed me. I am happy to look upon your face.
Shen: And I am filled with joy to have seen yours once again. Farewell, and go upon this last journey.
Kormac and Lyndon's interactions in Reaper of Souls. For much of the main game, it was clear that neither could stand the other, but after everything they've gone through with the Nephalem, they've finally started to forge a friendship...in their ownway, but still.
Best highlighted, in a quiet way, when you are embarking on Kormac's sidequest; he will ask the player to go with him, as he will need "a good friend" by his side. If Lyndon is currently set as your follower, he will chime in:
Lyndon: How about two?
During the final part of Act V, in order to help you challenge Malthael on equal footing, the souls of those he's imprisoned will aid you. Their spokesperson is always someone close to the Nephalem—the Demon Hunter encounters the spirit of their long-dead sister, the Wizard meets their most respected teacher in the arcane arts, the Witch Doctor speaks with the representation of their tribal heritage, the Monk reunites with the patriarch of their order, the Barbarian confers with a great hero of their people, and the Templar has a chance to speak with their predecessor. In all cases, the Nephalem show a softer side when talking to their long-lost loved ones, no matter how brusque, confident, or aloof some of them might be normally.
In Act IV, the joy in Eirena's voice when she finds out that the Prophet, who saved her and her sisters, and trained them to assist in defeating the Lords of Hell, was an Angel. Special mention, too, to the Angel that, as it lay dying, saw Eirena and reached out to her, giving her the text that contained the truth about her mission and her mentor.