I do believe there are some soft-erotic-ish games out in japan... I remember seeing one for girls actually, odd stuff. But I don't think there's any hentai games, and I doubt there will be any either. "Nintendo don't want it for the kids" isn't really a viable argument, since games like GTA is already on the DS, but it's a pretty narrow niche. It's not something you'd advertise on the bus or on huge billboards, exactly.