Tokyo

"Old Godzilla was hopping around Tokyo City like a big playground" - The Ultimate Showdown of Ultimate Destiny, Lemon Demon

Tokyo, of the Kanto region of Japan, is commonly known for being blown up, utterly destroyed,invaded by monsters, and the site of many a strange event.

Much of this is perpetuated by use of Tokyo for said things in anime and monster films. For this reason, when an author feels like doing a megacrossover and it does not involve Harry Potter or generally American characters, it is likely going to be an anime crossover and Tokyo will be the epicenter of it all.

If a fanfic takes place in Tokyo for no reason at all, it is likely that this is a badfic, or a contrived Humorfic.