So, my curiosity sent me browsing through Fanfiction.net for the oldest MadCom fanfics I could find, and the third oldest result on that page was this oneshot:
Madness Combat: We Used To Be One
And it's one of my favourite MadCom fanfics EVER now! It's a short but sweet read, and I really like how they characterized Hank with just a little over a thousand words. Recomended!
(Psst, by the way, if you got even older fanfictions or fanfiction websites, pass it over :P)