It's from her vivre card. It was such a throwaway design that he later reused it for a samurai in the cave.
She was also originally called "Ninigi" after the deity who was sent by the sun goddess as an emissary to Japan to bring civilisation, justice and order to humans.
https://mythopedia.com/japanese-mythology/gods/ninigi/
Not to mention her most prominent attack "Namuji Glacier", named after the Japanese god of nation-building and protective magic. Wonder what could be the meaning in all of that?
Real shame he didn't stick with the OG design though. Just imagine the Yamao cult attempting to enlighten us all on how humpty-dumpty over there is about to go on to become the sake brewer for the straw hats! Oh, right...without the Naminess n boobs, the cult would've never existed in the first place. Silly me.