WARNING: The following contains spoilers for One Piece Chapter #1016 by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English now from Viz Media.
Since O-Tama first arrived on the shores of Onigashima, she's really stood out in the war against the Beast Pirates. Chapter #1016 of One Piece is only further proof of this. Having reached the parlor level of Onigashima with the help of Nami and Usopp -- and secured the means of signaling her orders to the Gifters through a captured Mary -- the three of them now have a chance to drastically flip this war on its head, meaning that despite her age and unassuming personality, O-Tama has become a valued and irreplaceable participant of the current revolution.
Looking back, it really was appropriate that O-Tama was the first character Luffy met when he arrived at Wano and got separated from his crew. The young child painted a bleak picture of what life was like for the citizens of Wano under the cruel iron fist of both Kaido and Shogun Orochi. In Wano, even a bag of rice has become something to treasure rather than waste on a meal recklessly. And yet, the young kunoichi gave her's to Luffy so he would not go hungry, despite being starving herself. O-Tama had to go so far as drink polluted river water from one of Kaido's factories just to quell the pains in her stomach.
Needless to say, O-Tama quickly befriended Luffy and his crew, especially after hearing that the rubber man was Ace's brother. We also learned of O-Tama's Devil Fruit, enabling her to pull on her cheeks and make Dango pop off them. If given to animals, this Dango instantly makes them friendly to O-Tama, as demonstrated by Komachiyo and Hihimaru.
Once the pirates and samurai convened at the rendezvous point, we were led to believe that this would be the last we'd see of O-Tama until the end of the battle; but of course, Oda proved us wrong. With help from Speed, the centaur Gifter O-Tama befriended through her Dango, she was able to sail to Onigashima and has now ended up saving Nami and Usopp from mortal danger. Moreso, she made as much Dango as she could for Speed to hand out to every Gifter across Onigashima, making them all susceptible to her orders.
Nami and Usopp quickly realized that getting O-Tama's voice to reach all the Gifters in the performance hall was the key to victory, but bad luck hit them when they ran into Big Mom. However, when Big Mom suffered from temporary amnesia when she first appeared in Wano, it was O-Tama who helped her, which Big Mom remembers to this day. So, when O-Tama explained Kaido's men destroyed her village, the female Yonko's maternal-based morality made her turn on Kaido. She knocked out Page One with a single blow.
O-Tama is one of the smallest voices among the people of Wano -- a people who have been subjugated by Orochi's horrid rule for so long in One Piece. Her making such a vast difference in Onigashima means it's not just the Straw Hats who will save this land, but the samurai and people oppressed by tyranny as well, if not more so. Not only is O-Tama an endearing and likable character, but the events currently taking place in the manga would not be possible without her involvement.