Fallout Fionna: Vault Girl by buttsprincess
Don’t know how many people here are Adventure Time fans, but there was one episode that featured an entire gender-bender cast. Instead of Finn and Jake, it featured Fionna and Cake. I found this on deviantART and about had a nerdgasm.
Here is the original Fionna and Cake for those interested. (I apologize if the name is spelled incorrectly, the wiki says Fionna but Natasha Allegri is the original artist and she spells it Fiona)