So I was watching some conventions featuring Todd Haberkorn (voice of Natsu Dragneel) and Vic Mignogna (voice of Edward Elric). A question was presented to Todd asking what other anime universes he would want Natsu to jump into. His answer (in Natsu's voice): "Fullmetal Alchemist so I can burn Ed."
That sparked the idea for this drawing, plus the friendly rivalry between Todd and Vic.