Hello, everyone! Welcome to a new installment of my fanfic series Batgirl of the Future! Been a while since I've written one, huh?
This time, I'm going to be doing a crossover between Batman Beyond and Teenage Mutant Ninja Turtles. With TMNT, the 'verse will be a mix between the 2003, 2012 and IDW Batman/TMNT crossover series, but may be heavier on the 2003 side.
At this point, the title does not refer to an enemy within a group. Rather, it alludes to an enemy within oneself, and is a nod to a song that helped inspire this story: "The Enemy Inside" by Dream Theater. If you haven't heard the song, I highly recommend that you do so, as it's a magnificent work and has to do with an underlying theme of this story.
What's the underlying theme, WNR?
Post-traumatic stress disorder, also known as PTSD.
Anyway, this story also has a specific two-part episode from Batman Beyond wrapped in it: "The Curse of the Kobra."