I have absolutely no idea just yet what kind of storyline would be involved, nor any thoughts about genre, so that's all open for discussion.
My basic idea involves your character having a pair of living underwear that do all the things underwear are for, and love doing it. For example, if they had a telepathic bond, the underwear would be happy when he/she put them on, tell him/her how wonderful he/she smells today, etc. I also had the thought that since they would be living, they could have limited movement - such as being able to quickly constrict and return to normal - providing endless hours of vigorous hands-free masturbation for their wearer on command.
If you're interested in exploring this idea further, please send a PM!