This is not an adult comic because there's no "成年" mark on the cover. (so you get more censorship) This is what Japanese teenagers can legally get before they reach 18, although most of them actually already have access to adult porn. The reason for a non-adult release is that, they can be sold at places outside the adult corners in bookstores, thus having a much bigger group of potential customers. These kind of comics usually have better (or at least longer) stories. If you read Japanese, you can take it as a ordinary comic book with a lot of sexy scenes.