Oi there ^^
Well, by saying Oda's hints, I can be wrong, but I can be right too XD
Ok, it concerns the pairing zoro/nami, first of all : in Katakana, Nami is written ナミ=> na (ミ) and mi (ミ), if you look carefully, you can see that the "na" looks like a katana, and "mi" - in japanese it means 3 - looks like 3 lines, like zoro's earings/katanas ... even nami's weapon has 3 parts !
Other point, their hair colors : green and orange ... in fashion, it's known that the best color for red haired people is the green .. and about their birthday : zoro's sign of zodiac is scorpion, and nami's one is cancer, and in astrology, the pairing scorpion/cancer is the most succesful !!
Now just take a look at some Oda sama's works
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