User blog comment:Donutsonfire/What are you doing while you wait for new HOTD content?/@comment-3243210-20120506205800/@comment-3003168-20120816013723

I think it's just because Naruto is one of the most popular manga series in the U.S. right now. Five years ago you would've seen a lot of Bleach crossovers, and fifteen years ago it would've been Dragon Ball. HOTD has also become fairly popular (it was on the NY Times bestselling manga list) and appeals to the same teenage male demographic. I think fanfiction depends more on popularity than common themes, especially since writers can use the "magic portal" theory to explain how any character got into any type of world.