WARNING: The following contains spoilers for One Piece Chapter #1015 by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English now from Viz Media.
In Chapter #1015 of the One Piece manga, Nami's Climate Baton suddenly takes on a life of its own. This revelation comes after Zeus, one of Big Mom's Homies, gave up his life to protect Nami, Usopp and Tama as they ran away from Big Mom. For his efforts, he was weakened to the point that Big Mom took enough of his soul that Hera was able to consume him.
Up until this point, Zeus and Nami have had a close relationship since the Straw Hats captured him. Before this, Zeus was close to Big Mom, often feeding her when she craved food and fighting alongside her. He was the most powerful of the Homies because he was made out of part of Big Mom's soul, making their connection that much closer. He was also tasked with carrying Big Mom when she traveled across the sea, but after his capture, she saw him as useless and called him as such, threatening him if he went easy on Nami during the fight in Wano.
Nami, on the other hand, treated Zeus as a friend. He lived inside her Climate Baton, which he said was rather comfortable for him until he was captured in Totto Land after Brook brought him back to the Thousand Sunny. Nami threatened Zeus saying that she would kill him if he didn't act as her servant, to which he agreed. However, Big Mom was able to take back control over Zeus and berated him for helping the Straw Hats. Because he was now fighting against them, Nami declared that he was no longer her friend.
Despite being a part of Big Mom's gang once again, Zeus felt guilty for having to fight against Nami, but he knew he would be killed otherwise. He was trapped in a box by Captain Kid and Trafalgar, after which Big Mom frees him and calls him useless for not saving her from falling from the roof. This was when he met his replacement, Hera. Big Mom weakened Zeus so that Hera would be able to consume him and gain his powers, just as Nami was running by. He called out to her, but it was too late and he was consumed by Hera.
But in Chapter #1015, after the announcement is made that Luffy is still alive and plans to return to battle, Nami's Climate Baton suddenly begins to talk, saying it's glad that he's still alive. Upon inspection, the Baton now has a face that resembles Zeus', implying that some of his soul remains within it. How this was made possible and how it will affect the power of the Baton are still unknown in the One Piece manga, but it could very well make Nami susceptible to Big Mom's powers.
