At last, we reach the finale of... err... Finale, and Yuuto has some work to do as the news breaks that his beloved Haruka has effectively been kidnapped with a view towards an impending forced marriage.
Luckily for Yuuto his rescue attempt isn't going to be a lonely one, as effectively the entire cast of the series to date crop up to lend him their support - very necessary support it is too, as Haruka is being heavily guarded in the run-up to her wedding. Thus, most of the episode is spent with various members of the cast and groups "sacrificing" themselves in the name of protecting Yuuto and allowing him to continue his quest, while also confessing their love for him where appropriate (or, in some cases, mildly inappropriate depending upon how you look at it).
All of this leads up to a final "boss fight" for both Yuuto and Haruka as they face-off against Haruka's parents, at which point of course their love shines through and leads them to victory before it's revealed that this entire scenario was simply a test devised by said parents to ensure that this couple were suitable devoted to one another. Because Haruka's parents are assholes, clearly. Still, our main couple get to live happily ever after, and we get to finally put this franchise to bed - so everyone wins at the end of the day, right?
In fairness to Nogizaka Haruka no Himitsu, at least it offered up a proper conclusion to its story without any of the doubts or cop-outs that tend to plague harem shows of this nature. Of course, this doesn't stop the show as a whole from being anything but utterly mediocre with only occasional flashes of anything resembling fun, and even those moments were basically entirely absent from this OVA which simply piled some fan service on top of some utterly tepid story-telling in the hope that nobody would notice that the whole thing was a bit rubbish. Sorry guys, but I did notice - then again, I watched over eleven hours of this series, so I guess those involved in its creation get the last laugh this time...