Here we go again...
Isaku is supposedly the evil janitor Shusaku's older brother. From the credits alone, one can see that this is a much older anime, released 1997-1998. I can't actually say anything here that I haven't before mentioned in Shusaku. Meaning, I can't really count how many times I have professed absolute disgust at scenarios where every supposedly intelligent girl gets manipulated by one very ugly janitor. And I must say, Isaku is uglier than Shusaku.
The atmosphere here is very different from Shusaku, nevertheless. You start off believing that it's one of those light-hearted fare, where a school setting is dominated by hormonally imbalanced teenage males worrying about the girls of their dreams. The boys are characteristically cheerful and the girls are a bit more bouncy than your regular sexual horror victims. The women, however, aren't any less idiotic than the victims of most blackmail-oriented themes. I mean, just imagine, would you actually go off on your own to pee, separating yourself from your group, when you know that some maniac has been kidnapping girls in the building?
Isaku himself is more of a passive observer in the beginning, unlike his brother, who hogged all the action right from the second your DVD plays. Furthermore, while Isaku holds the title, the protagonist seems to be this useless, wimpy young boy named Kenta. Kenta, who has the personality of a worn-out doormat, appears to be the object of his classmates' fantasies. Why the writer felt he had to insert a self-important Tenchi/Keiichi knock-off in a hentai title, I have no idea. He doesn't even get laid, for heaven's sakes.
There are a couple of antagonists in addition to the janitor. Unfortunately, if you thought that they might be hiding a deep dark past, which might account for the reason why they hate women with so much passion, you just might find yourself disappointed. You will never know what motivated them to rape, torture, bind, and force their hapless victims into submission. It's just implied that there might be something more than meets the eye.
The artwork is good, obviously from the pre-digital age, but it has that classic look that I find very attractive. Hentai scenes are moderate and not nearly as nausea-inducing as most recent titles are. Of course, since Isaku is Shusaku's brother, the volumes would never be complete without enema. That being said, the only saving grace this has over Shusaku is the fact that the scenes of female abuse are much milder and not nearly as graphic. Funny thing is, even with that advantage and the nice art, Isaku is still something you can add to your crap list.