For a long time, she lived a normal life, but once she was upset with Bell-mère and her sister went after her, neither knew about a New Merman Pirate Group that took over their whole island.
All the citizens were forced to pay for themselves, 100,000 for adults and 50,000 for kids, but since they were poor, Bell-mère only had enough for herself, in other words, 100,000. Hence, the chief of their village told her to pretend that she had no children, but instead, she said to them that the 100,000 Beli (One Piece currency) are for the two of her daughters, and then they killed her.
Arlong, the captain of the pirates’ group, was impressed by Nami’s map-making skills and kidnapped her.
There he offered her money for making maps for him, but obviously, she refused, so he promised her that if she saved up a hundred million, he would give her freedom and let her village go.
After knowing that, she joined the New Merman Pirates to save up money, but since that wasn’t nearly enough, she also started joining other pirate groups earning their trust rather than taking their money and betraying them.
After eight years of saving up, she was finally almost done. She had just 7 million left until it was complete, but Arlong didn’t want to lose such an essential member of his crew. Therefore, he sent a corrupted marine officer that he was working with to go and confiscate all the gold.
Angered because they tricked Nami, all the villagers finally decided to go up against him.
Though mermen are naturally stronger than humans, they had no chance.
Luckily the Straw Hat Pirates were there at the time since Nami just betrayed them but were there to get her again.
Sure, it was not easy Luffy defeated Arlong and Nami became a member of the straw hats again. The victory also gave Luffy his first-ever bounty of 30 million.