Aika R-16 exists purely to deliver fanservice with zero apology, and it moves fast enough that you don't have time to notice the plot is basically a framework for the next scene. The character chemistry between Aika and Erika is genuine, which somehow makes the entire thing work despite the fact that nothing here makes sense. The animation is sharper than it has any right to be for an OVA this committed to its own shamelessness.

Aika just earned her salvage license, a C-class one, and she is ready to prove she belongs in the salvaging business. Problem is: nobody wants to hire a hotheaded teenager, no matter how capable, and even Gota still sees her as a kid. So she takes matters into her own hands, advertising her services around school until she catches the attention of Erika, the rich heiress who runs the treasure hunting club. Erika wants something recovered from the sea, and Aika happily signs on. But once she spots the cutting-edge submarine aboard Erika's private cruiser and learns where they are headed, Aika understands just how risky the job really is. The trip leads to a showdown with a band of armed high school girls in the southern islands, and a mysterious girl named Karen enters the picture. Expect a three-episode OVA mixing action, comedy and ecchi fan service.