This is illegal. In Australia hardly any anime is released and never the best shows, if you want the best of anime, fansub is the way to go. Unfortunately our society has a habit of focusing on the negative, and this is a sad example. Hentai's main audience aren't interested in Anime at all. Hentai is frowned upon by many fans.
Themes range from every imaginable possibility and more.
The animators have no constraints and can draw things that 'live' films could never achieve. Fantasy and science fiction is probably the most popular theme and many shows feature this including the famous 'Escaflowne of the Heavens' and 'Neon Genesis Evangelion'. Mecha or Giant Robots, is also a popular theme, practically the titles 'Gundam' and 'Macross'. Modern Drama is one of my favorites. Black Jack' and 'Perfect Blue' are two recent drama films that are making a splash also.