Square Enix just opened a new teaser website for a “secret” new game, as indicated by the site’s url “http://www.jp.square-enix.com/secret/“.
The reveal seems to be coming on April 13rd. If you use the facebook link on the top left of the site, it will in fact share “Square Enix New Project NEXT 2015.04.13.”
At the moment, your guess is as good as mine on the actual nature of the game. No further info has been shared about title, platform or basically anything else.
The only hint is a sequence of apparently meaningless letters and numbers “S A R 0 1 0 1,” which are probably part of a title or message that may or may not be completed over the next few days.