It was a hilarious OVA.
The plot essentially starts with them getting stranded on an island after a plane wrecks the ship they were on when going on a field trip. The way they animate this is so comical that at this point you understand the purpose of the OVA. It does not want to deliver a compelling story whatsoever. It's just here for pure comedy and fan service.
The rest of the special focuses on a game where if one of the girls has to try and obtain the special red badge that Haru has, and if they do they get their wish granted. All the
other girls have yellow badges, and if their badge is stolen they're out of the game. Now it's up to Azuma to help Haru keep her badge.
One thing I like is how the OVA knows that this is a stupid premise. Haru even mentions many times the major fault with it. No thought at all was put onto the premise of this OVA.
Now onto the fan service. The fan service was used to full effect here. The fan service was used purely for comedic purposes. We mostly see characters stripping each other for no good reason, and while it's happening I was just wondering "What the fuck?" It was great.
Overall this was a fantastic OVA. It made a ridiculous premise and took it in unexpected directions that were sure to satisfy the audience.