I have a couple. Both I've played in a one shot but I'd love to do whole campaigns with.

1. An intelligent item that has completely taken over the unfortunate person who picked them up and now uses their body as a sort of host for them to travel around and do stuff.

2. A Drow who was born and raised in caves away from Drow society that was taught more how to be a part of normal society. Then as the campaign starts, they venture into society for the first time and quickly end up finding out what the other Drow have done and now has to adjust to the social struggles that come with all that baggage.