Talk:Natsu VS Ace/@comment-3391158-20170419140554/@comment-4970402-20170419152056

They've gone on record talking about how long it takes them to watch through long-running animes for research. Due to the time it takes, they basically take down information for all relevant characters as they do so, anyone they think might get a match in the future.

In his case, their research time for Zoro vs Erza also provided research for Natsu vs Ace.

Why they chose OP and FT over other animes to research is likely because these two have the most matches they are interested in, particularly with eachother. Watching through all of Bleach and Naruto would be a waste if the only match of either series is Naruto vs Ichigo. They'll still get around to such matches, but in the meantime they're putting out a match they basically have been sitting on the research for.