Square Enix is teasing some kind of mystery game -- in that the identity of the game is a mystery, not that it's about solving mysteries. We don't know; it could be that too.
What we do know is that the teaser site has the URL "cc2012.square-enix.co.jp," which may be a clue. The video features fantasy-style characters, crystals, and art by Castlevania: Order of Ecclesia artist Masaki Hirooka and longtime Square artist Yusuke Naora. It's also given a "summer 2012" date.
Our guess is that it's some kind of new mobile/iOS RPG like the Chaos Rings series (on which Naora works). We'll find out more when Square Enix is ready to stop teasing us.