Japanese history is voluminous. And there have been huge changes. Just look at this past century! But domestic game company Square Enix and Yahoo! claim it will change Japanese history.
A teaser site on Yahoo! Japan reads: "On May 21, we'll change Japanese history." So when you buy a Japanese history book in 2011 or 2012, it mention May 21, 2010 - the day Yahoo! Japan and Square Enix changed Japanese history.
The teaser site also has a Twitter feed in which folks can predict what the reveal will be: From a Dragon Quest MMO to search engine game. Be sure to check back tomorrow when history is made.