Uzu is one of the children kidnapped by Caesar Clown and treated with the NHC10 drug.
At first glance, Uzu seems like a normal child. But because Caesar Clown has experimented on him and the other children, he is as tall as a giant’s child. Uzu seems to be one of the tallest children even with Sind and Mocha. He always has his eyes closed and dark curly hair. Before Caesar’s treatment, Uzu had a normal head, but since the giant growth, his head has become so thick that you can barely see his neck.
Uzu, along with Mocha, Sind, Doran, and Konbu, were among the first children kidnapped by Caesar, which is why they were the tallest. He, like the other children, fled with the Straw Hat Pirates when they accidentally entered the Biscuits Room.
When they took shelter in a cave and Sind started hallucinating due to withdrawal from the drug, the same thing started happening to Doran and Mocha right after, followed by Uzu. As a result, the Straw Hat Pirates had to put them to sleep and put them in chains. However, when they woke up some time later, they managed to break the chains and attacked Nami and Usopp, who were still there to guard the children. Caesar had also arrived by now and took the children back to his lab.
There, the children were supposed to get candy again, but this was prevented by Chopper, who was able to sneak into the lab, and Mocha, who came back to her senses. Uzu and the other children then chased Mocha, who in turn tried to keep them away from the candy. When Mocha, out of desperation, ate all the candy herself and then collapsed, the G5 Marines took advantage of this to inject the other children with a sedative on Chopper’s orders.
After the successful escape from the lab, Law treated all the children to rid them of the toxic drugs as best he could. Later, the children were to be returned to their parents by tanker. The children would have liked Nami to take them back, but Tashigi took over that task. At the beginning the children were not so enthusiastic about it, however, they could be convinced then, nevertheless, still.
After Doflamingo’s defeat on Dress Rosa, Tashigi informed the children that they would soon meet Dr. Vegapunk.