Nintendo Japan is changing the packaging for its “mature” Cero C (15+) titles. Instead of the usual white cases, the games will be packaged in black boxes. The move isn’t required by the government, rather it’s Nintendo’s own initiative. The change is as a result of Nintendo introducing its first Cero D (17+) rated game in Japan, Zangeki no Reginleiv.
For what it’s worth, I think the black boxes look pretty cool. It hasn’t been revealed whether Nintendo of America will make the change as well.