The cartoon image of a voluptuous 17-year-old aspiring "ama" diver in search of a boyfriend drew fire from the real divers, who traditionally harvest seaweed, clams and, in some areas, pearls.
About 170 people, mostly female divers, have signed a petition calling for the city to scrap the character, according to a tourism official in the coastal city of Shima 300 kilometres south of Tokyo.
Protesters reportedly said the mascot, launched late last year, was obscene and sexist.
Cartoon images of young women with exaggerated body features are common in Japan and have attracted criticism.
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The mascot spat also comes just weeks after Tokyo's 2020 Olympic logo triggered plagiarism claims due to its resemblance to the logo of a Belgian theatre and a separate Spanish design.
"We may consider changing the mascot's design to avoid hurting some people's feelings," the Shima official told AFP.
"But at this point we have no plan to retract our official approval for the character."
"Most of the reaction we've received from the public so far has been positive," she added.
Mascots representing local municipalities have surged in popularity in a nation obsessed with all things cute, amid hopes they can promote ageing and declining rural communities.