>>4143617They started off as nondescript bad guys and gradually started moving towards being fallen(sunken?) versions of shipgirls. The direct counterparts vary from borderline palette swaps like Escort Water Hime and Gambler Bay to slightly more abstract, like Northern Water Hime's hat referencing Gangut's smokestack or Abyssal Jellyfish Hime referencing Saratoga's overgrown wreck. There's a few that are also loose amalgamation of two or more ships from what I understand.