Ryoga wants some time alone with both Akane and Akari, but a magical umbrella complicates the love situation even more. Then, Akane and Miss Hinako race to see who can learn to swim first, Ranma nearly dies from food poisoning, a cursed doll possesses Akane, and they all get shipwrecked on a deserted island.

Akane Tendo is shocked when she wins a contest by being the 10,000th girl at the beach who isn't able to swim! The locals reward her with an enchanted jellyfish bathing suit that has the uncanny power to enable its wearer to swim. In return for this prize she must enter a long-distance swimming competition against a group of girls all wearing the same magical bathing suit. Akane takes the lead, but a dangerous surprise awaits her at the finish...