I don't think this is a Hentai work as defined by Mangadex guidelines. It was serialized as R18, sure. However, Mangadex defines Hentai as a work where most of the focus is on sex. By sheer page count, the sex accounts for only about 30% of this series (Chapter 2 doesn't even have any, just two pages of partial nudity). The focus here is very clearly the story. They spend nearly an entire chapter hashing out the details and drama of the island girl's family situation. In a Hentai work, that'd only happen in preparation for an incest scenario (obviously that doesn't happen here).
As an aside, I found this series to be quite good. I'd give it a solid 8.5 rating if I could.