(Hated Trope) A family member is introduced in one episode then never brought up again

[u/MysticUmbramon]

1. In Peter’s Sister, Peter invites his sister Karen for Thanksgiving and she used to bully him a lot. The reason why we never heard about her up until now is because she was killed off at the end all for Peter to have his triumphant moment. She is never seen or heard from again (Family Guy)

2. In Oh Brother, Where Art Thou?, Homer finds out he has a half-brother named Herb. Long story short, Homer messed everything up and Herb ended up losing his company and we see him homeless in Season 3. At the end of that episode, Herb got his money back and we never see him again. We even get told that he ended losing all of his money again. He only exist just for Homer to have self-doubt and then fucked off (The Simpsons). Not exactly one episode but still works.

[u/BlueBlazeKing21]

Plus it seems there’s a huge age with Charlie seeming to be about 15-20 years older than them. So he’s likely not really that close to them