Like death and taxes, it's a sure bet people watching porn, even the animated variety, aren't watching for a storyline.
But those that do will be rewarded with an interesting, though convoluted, story with Shusaku Replay. This is not lovey-dovey, couples friendly hentai; within the span of the opening three minutes of Vol. 2, there's coerced sex and urination. Like the other volumes of the series, the story revolves around a blackmailing janitor at an all-girl school.
Though Vol. 2 is decidedly raunchier and hardcore, the final two volumes of the series slowly begin to coalesce elements of the story together until, in the final episode, we see the reason for the insanity.
Good selection for fans of the rougher and more toilet-inclined animated stuff.