The Cursed Bathing Suit is the spirit of a bathing suit that was rejected during a date with it's original owner's lover, Natsuhiko. It has since been waiting at the bottom of the ocean for Natsuhiko to compliment it. Should a woman breaks its seal they'll be forced to wear the suit and be dragged back to the ocean at sunset should they have failed to get a compliment for the bathing suit from Natsuhiko.
Several decades prior to the events of the series, the Bathing-suit was worn for the first time by it's original owner on a beautiful summer's day. Natsuhiko was meant to compliment the swimsuit while he was on a date with the original owner, but instead offered another (and, in Natsuhiko's opinion more attractive looking) swimsuit, causing the swimsuit to be thrown away. Since then it has rested underneath the ocean in a shrine, where it will produce an illusion of a dog and attack young girls who swim near it. Should the girl break the shrine the swimsuit will be stuck to them, and should they fail to get a compliment from Natsuhiko by sunset the swimsuit will return to the ocean with the girl, where she'll drown.
One day Ranma and the others had gone to a beach where the swimsuit resides near. Once there they learn of the "dog" that haunts the water, so Ranma is sent by Soun to sort things out. Almost immediately, Ranma finds the so called dog and begins to fight with it. However, Ranma soon realises that it's just an illusion and sees a small shrine on the seabed. Ranma breaks the shrine and a bright light shines out, and Ranma looses consciousness.
When Ranma awakes, she find herself wearing the Cursed Bathing Suit. Ranma tries to get it off, but the suit won't budge. Genma then tries to use Scissors to cut the swimsuit off, but the swimsuit suddenly bites the scissors, chews them and spits them out again. The swimsuit then begins crying and explains about it's history and what happens should one be unable to get a compliment from Natsuhiko.
The group quickly goes searching for this "Natsuhiko", they don't have to search long as the old man who talked to them earlier happens to be Natsuhiko. However, when Ranma tells him to compliment her swimsuit, he asks if she wouldn't like another one which he offers her instead. Natsuhiko eventually compliments the swimsuit, however, the swimsuit doesn't recognize Natsuhiko as he's aged during the years it's been under the ocean. As the others worry about what they're going to do, Kuno walks in (initially covered in seaweed) and the swimsuit says that he's Natsuhiko.
At the sight of who it believes to be Natsuhiko, the swimsuit rushes towards him (dragging Ranma along in the process). However, Ranma kicks Kuno and knocks the seaweed from his head, meaning everyone is able to recognise him. Ranma quickly gets to work flirting with Kuno so that he'll compliment the swimsuit. Unfortunately, when Ranma asks Kuno directly to compliment it, Kuno declares that he can't compliment such an ugly design. This upsets the swimsuit greatly, so when Kuno tells his pigtailed girl that she should wear a special swimsuit which he made for her (that happens to have Kuno's face on it, surrounded by roses), the cursed swimsuit gets extremely angry and eats Kuno's swimsuit.
This upsets Kuno greatly, who begins to run home along the beach. Ranma gives chase and the pair eventually tire. Kuno reiterates he's not going to compliment the swimsuit, causing Ranma to say she'll go on a date with him so he'll stay. The next day and the pair have a very fun date. Ranma then tells Kuno there's one thing he hasn't done yet, and that's tell her how pretty she looks in her swimsuit. Kuno quickly changes the subject, angering Ranma, but the swimsuit tells her not to be mad at him as the day it was cast away the suit was going on a date with Natsuhiko and it's so happy to finally go on a date.
The others take these comments as meaning the suit is content and will leave Ranma, but as the sun sets, the swimsuit starts returning to the ocean and is still taking Ranma with it. The swimsuit explains that it was fun, but it still wasn't complimented. As Ranma is being dragged into the ocean, Kuno chases after her and says he was being petty as her swimsuit destroyed the one he made. Kuno continues by catching up to Ranma and saying that her swimsuit is one of the most beautiful he's ever seen.
Having finally being complimented by "Natsuhiko", the swimsuit is content and so passes on (leaving a blushing Ranma naked in the ocean in the process).
The swimsuit seems to not have many abilities, beside those which relate to it's curse. However, the swimsuit is shown to be able to project the illusion of a dog-like creature while it resides in it's underwater shrine. While attached to it's victims the swimsuit is also able to talk fluently and bite/consume objects should it feel angered or threatened.
Despite being the reason for the swimsuits original disposal, the swimsuit seems to hold no hard feelings towards him and is just concentrated on being complimented by him so it can finally pass on.
After cursing Ranma to wear it, the swimsuit seems grateful that Ranma is so willing to help it pass on.
Given Kuno's resemblance to Natsuhiko during the time which the swimsuit remembers him, the swimsuit is very tolerable of Kuno as shown by how it tells Ranma not to get mad with him shortly before reminiscing about being meant to go on a date before being cast aside.
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