The good ending of the quest "Beauty and the Beast" in the first game. Carmen is moving mountains to find a remedy to cure Vincent, a werewolf. Geralt finds three remedies, and when the first two don't work, Geralt mentions the third: true love. Carmen is convinced that Vincent doesn't love her because she's a whore, but when Geralt goes to Vincent and tells her, he's willing to give it a shot. It works, and they get married.
The simple fact that Carmen, a frail city girl with her puny dagger, dares to go to the monster-filled swamp, despite being obviously nigh-paralyzed by fear—all just to help the man she loves, is extremely heartwarming.
If Geralt decides to cure Adda of the striga curse again instead of killing her, there will be a small cutscene in which Geralt says that although witchers are renowned for slaying monsters, they (or at least, he) take far more pleasure in lifting curses and breaking spells on people. Even more heartwarmingly, said cutscene ends with a bright, colorful picture of Adda and Radovid obviously Happily Married.
A potential solution to "In The Heat Of The Day" can be one too: If Geralt defended Abigail against the mob in Chapter I, she suggests poetry to put Alina to rest. Dandelion whips up a poem at dusk, and after Alina understands that she's dead and a noonwraith, her sister (now a nightwraith) shows up, and begs forgiveness for killing her. Alina forgives her, the two reconcile, and Alina moves on to the afterlife. And if you completed "Hunting the Wild Hunt" and asked for the Wreath of Immortelles, you can put Celina to rest too.