[Trope Discussion help] First Girl After All

[sakabatou]

3. The story has been presented already, so I'm going to use a generic example

We have a long running animated show, with well known characters with rotating cast that changes every so often. We have the main character (let's call him Aaron), and two rotating characters. In a VERY late season, one of the new cast is Amy. Amy turns out to be Aaron's childhood friend, who has a crush on Aaron.

Aaron doesn't remember Amy whatsoever. Amy has also never been mentioned in passing in previous seasons, nor has ever been referenced to, nor even been implied to be a childhood friend of Aaron. Not even as a possibility.

In dialogue, Aaron could have said, “I’ve had lots of friends when I was younger, but many have moved away.”

This would give Amy the possibility of being Aaron’s childhood friend. We don't get any kind of line like that in the show.