To distinguish mature (CERO C/15+) games in Japan, Nintendo will be using black cases instead of the usual white/red options.
The upcoming Zangeki no Reginleiv will be the first to ship in the new black box, after other 15+ titles - like Resident Evil, No More Heroes and Onechanbara: Bikini Zombie Slayers - sold in the regular white box.
The move comes in addition to large CERO stickers emblazoned across the box and on store shelves - to try and scream to parents that the contents will not be suitable for their young'uns. Games, films and other media aren't required to come in distinguishable boxes, so it looks as if Nintendo will be starting a trend for other publishers.
Thanks to Siliconera.