[Reid]

Video Girl Ai isn't hentai, though it has nudity and lot's of sexual themes.
Masakazu Katsura's manga usually revolve around teenage/young adult love as the theme so to be realistic in the scenes he has sexual situations (even though they can be a bit gratuitous at times) in them.
His story telling and art really is great though, so if anyone here wants to check out more of his work I'd really recommend I"s (Dna^2 and Shadow Lady are also good, but not as much).