Clicking that link leads to a gallery with several clips from Imma seiden, you can see the full movie on streaming video via pay per view. (This site uses licensed content from the studios so you’ll be supporting the industry if you do, unlike p2p downloads, heh like anyone cares)
I don’t watch that much hentai anime, even though I produce hentai animations myself I usually read manga and dojinshi instead. Most hentai animation is rather poorly produced and low quality, but Imma seiden is a cut above the rest. The animation quality is good and it actually has a plot.
In fact it is very similar to a hentai version of Mai Hime, that is, it would be if it wasn’t actually an older series, so maybe Mai Hime is actually a mainstream version of Imma Seiden. This isn’t as unlikely as it sounds considering how things in japan make the jump from porn to mainstream far more easily than they do in the rest of the world.
The setup is the typical “school full of pretty girls where evil monsters lurk”, the girls have special powers and aren’t complete pushovers, and sometimes they manage to avoid getting tentacled which makes for a bit of tittilation. The tentacle scenes are well animated and don’t cop out with the “magical clothes ripping” shortcut other movies in this genre do to save having to animate complex stuff like clothing + tentacles. Also there is no excessive gore/body deformations like in other more recent tentacle animes which I find to be a turnoff.
The girl in the sample gallery has a little batlike pet that transforms into a giant monster when she needs protection. The monster wants to rape her but since she can control his transformation she can turn him back into a harmless form whenever she wants. I haven’t seen the episode those clips are from but I’m guesssing her classmates are being controlled and she doesn’t want to use her pet monster because he would kill them, so…
All in all it’s a pretty fappable show that won’t insult your intelligence while you’re watching it. Contains tentacles, monster and human rape but no dickgirls, at least in the first 3 episodes.