Not to say that the other Corpse Party games are for kids, they aren’t and in Japan all of them are rated CERO D for people 17 and up. Even though Corpse Party The Anthology: Sachiko’s Game of Love – Hysteric Birthday 2U is supposed to be a love comedy… it also might be rated CERO Z. Titles with a CERO Z rating are highly restricted and bear an 18+ restriction, essentially making it like an "adults only" game in North America.
What’s unusual is Corpse Party The Anthology is rated CERO D as a standalone game, but the product page says the limited edition is under review and will probably be CERO Z. The limited edition includes a DVD called Corpse Party: Missing Footage. I suppose whatever’s on the disc is pretty grisly since that’s the main difference between the two.