It's not really something devs have in mind.
I mean, I had to personally convince Arc to give Claire freckles on her body, since she used to only have them on her face.
I know Kana and her mother have a birthmark in the butt.
And one of the kunoichi had a mole in her breast.
But don't think this will be common, nor something that would make sense to add retroactively.
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Masako (horny one that wears purple) has a mole on her left breast, but it's barely noticeable.
And as I said, it probably won't be a common thing, because it's a matter of Arc remembering to add them while creating the characters. And adding them later wouldn't make that much sense in my opinion.
I will push for freckles whenever I can.
Already got Claire.