Pure smut, nothing more, nothing less. Some semblance of plot is the set up for several explicit scenes of incest, rape, masturbation, etc. The characters are stick-thin in terms of depth and rely on one or two personality traits throughout. There is of course a possibility for a story like this to explore deeper questions, but that is really out of this manga's league (this is just a story of constant lust), see Koi Kaze for a more serious look. I know this manga is defined as an "ecchi" manga but it's more or less hentai.