my first mxm pairing has got to be heeroxduo.
i remember when i was younger, everytime i watched GW i would always think to myself that heero would look so much better with duo. it also helped that i found relina very very annoying. so they were my first true boy x boy obsession. after awhile i started getting into yukixkyo -- and kyoxyuki fanfics i love both types-- from fruit basket.