There's a lot that can be said about Nami. She's emotional, sympathetic, persuasive, and loyal to her friends. All of these things are also indicative of her Zodiac sign.
Nami was born on July 3, making her a Cancer. This is actually meant as a joke as the kanji for seven (七) and three (三) can be read as na (ナ)and mi (ミ) respectively. Regardless, there is some astrological meaning that can be derived from it. Many things Nami does throughout One Piece can be considered traits of someone born a Cancer. To prove it, here are some characteristics associated with The Crab and how Nami represents them.
Cancers are deeply intuitive and sentimental. As a result, they can be difficult to get to know on a personal level. When someone finally does form a connection with a Cancer, however, they will remain passionate and loyal. Cancer's earned loyalty is meant to be viewed with regards to love, but it can also apply to Nami becoming a Straw Hat Pirate. When she first "joined" the crew, it wasn't meant to be permanent. She only stayed on board as a means of achieving her personal agenda. It wasn't until the crew saved her hometown from Arlong's reign of terror and Luffy declared her his friend that her trust was earned. She has remained a faithful and reliable member of the crew ever since.
Nami's loyalty and zodiac sign can be further explored through her relationships with her friends and family. Cancer's are filled with respect for people with whom they can easily communicate. They mainly enjoy socializing at home, a place of intimate atmosphere and deep understanding. These traits can be observed in Nami's interactions with the other Straw Hats, all of whom treat one another like family.
Cancers also share a deep connection with their actual family. Among all the zodiac signs, Cancers care the most about family. They are deeply sentimental and preserve memories of their family for years. Nami may be an adoptee, but it's unlikely that she'd forget the good times she shared with her sister Nojiko or their mother Bell-mère any time soon. In fact, she kept three mikan trees from Bell-mère's grove with her aboard the Thousand Sunny. As far as career choices are concerned, Cancers are also loyal to their employer, which, in Nami's case, would be Luffy. This was exemplified during the raid on Onigashima. At the mercy of Ulti, Nami was given the choice to either die by headbutting or admit Luffy wouldn't become Pirate King. Even in the face of death, the Straw Hat navigator compulsively claimed her captain would become Pirate King.
Another noteworthy aspect of Cancer's career path is how they handle their earnings. Cancers place great importance on earning and saving money, which is part of why they work so hard. They're often put in charge of finances in their household. They must keep their family in check and make sure that whatever wealth they've accrued is spent wisely. Everything about Cancer's handling of money describes Nami to a T. She initially became obsessed with money for two reasons; her poverty-stricken childhood and settling a debt with Arlong. Since then, her eyes have often turned into Berry signs at the prospect of a huge payday. She's also in charge of the Straw Hats' finances and gets violently angry when they spend a lot of it, especially when it's done behind her back.
It's important to remember that Nami, despite her attitude, knows how to prioritize her friends over her money. A good example of this comes up during the Straw Hats' time in Water 7. She found Usopp beaten up with the crew's money stolen, but was more concerned with his well-being, and insisted that the money doesn't matter. Empathy is another strong suit of Cancer. For Nami, friendship beats out personal gain wherever it counts.
There are other ways Nami embodies Cancer, but these are the biggest ones. A key takeaway from all this is that Cancer requires patience and love to nurture their empathy. Fortunately, Nami has made plenty of trustworthy friends and constantly does her best to return their kindness.
