It's not from any of the plots, however. Any Pound Chat regular should know the story of Gwen, a blue Uni, who was being transferred between accounts. The transfer was canceled, but Gwen's owner's account had been deactivated, so she was stuck in limbo until the admins got around to solving her problem. Many a PC-er wanted to adopt her, many of which only did so because of her plight. This troper isn't too sure about the details, but Gwen is now happily adopted, morphed into a Gold Draik, and it's clear her new owner loves her very much.
The Plots seem to have many of these, one being at the end of The Faerie Ruins comic.
Numerous Advent Calendar animations have these if they don't fall under Funny. One in particular (Dec 9 2013) features a class with one sleeping student. Instead of admonishing him, the teacher instead gives him a present…which contains an alarm clock. The smile the teacher gives is quite sweet.
For the 2014 April Fools' Day prank, pets from the pound were randomly distributed among accounts as foster pets for 24 hours. The first thing many users did on April 2nd? They went right back to the pound to get at least one of them back permanently.