Masculine or feminine? A name such as "Naysha" could be of either gender, and could also be found among many different cultures.
You get points for at least letting us know that you tried to find out the name's ethnicity, and just don't know.
Most obvious (to me, at least -- others here may have other ideas) would be that this is a Slavic pet name for "
Agnes" -- sometimes spelled "Neysha".
Click on the blue hyperlink --
Agnes -- for meaning.
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Nanaea