This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Neverwinter Nights
The section of the original campaign in Charwood gradually becomes one as the PC discovers what happened there.
In Hordes, the Sleeping Man's True Love is randomly determined. If it turns out to be the Sensei, get the tissues ready. The Sensei has devoted her entire life to worship of the Sleeping Man and truly is in love with him. When you awake him and tell the two of them that she is the True Love he's been waiting for, she panics, not ready for a closer relationship , and teleports away to parts unknown leaving him to follow.
Opting to kill Aribeth instead of convincing her to submit herself to Nasher's judgement in the original campaign, and convincing her to remain as a blackguard in Hordes. To see a paragon of justice being broken and converted into an evil being is heartbreaking.