If you don't know who the character is and can't find any information about them, then you should use character request instead of using a different copytag. In this case, the Pixiv image was also tagged with the main character's name in Japanese, which you can verify by looking at that character's wiki.
If there is an explanation for this i would like to read it, feels like is a classic devs not keeping with the times or just making bad choices, tho so far im only aware of the bad choices they made during events.
Removed kasumi kai ni swimsuit mode tag since this predates her official swimsuit, and is not kai ni (as evidenced by the mast in her hair ribbon). This was just a really good guess at what her official swimsuit would be.