Momonosuke is an inhabitant of Wano Country and the son of Kin'emon. He ended up on Punk Hazard after stowing away on a ship. He was first mentioned when Kin'emon told Sanji that he came to Punk Hazard to rescue his son. His name was revealed when the samurai was asking if the captive children in the Biscuits Room had seen him. In his first appearance, Momonosuke was seen in his full animal form, an Eastern dragon with a long, pink, slender body. This form has yellow eyes, horns, and scales along his back. In his human form, his appearance matches the stereotype of all samurai found in ancient Japan, with a topknot and the top of his head shaven. As a child, Momonosuke is quite short. His father used his Devil Fruit ability to give him a pink kimono with peach designs on it, matching his name ("momo" means "peach" in Japanese.) He also wears a red scarf, a purple obi, and a pair of geta.
Momonosuke has a prideful and stubborn personality, as he was unwilling to communicate with the other kidnapped children due to his status as a samurai. He also refused to eat any of the food or candy they offered him. Ironically, this attitude is what prevented him from getting poisoned by NHC10. Despite his pride, he also cried when he thought his father had died. He claims that he is the man who will become the Shogun of Wano Country. He also claims that he is not afraid of anything and even threw a fit when Luffy asked him if he is afraid of heights. However, he is terrified of Doflamingo after having witnessed his cruelty. Despite his pride and stubbornness, Momonosuke did not deny his fear of him. Despite his age, he seems quite interested in older women like Robin and Nami and has used a combination of fake innocence and flattery to get the women to treat him maternally, allowing him to get away with things for which grown men would be considered perverted. While it initially appears he really is just innocent, the look that he gives his father, Brook, and Sanji makes it clear that he knows what he is doing, clearly showing a perverted nature on his part. When he was in his human form, before consuming his Devil Fruit, he was seen wearing a sword, although it is unknown how skilled he is at using it. Momonosuke ate Vegapunk's man-made Zoan-type Devil Fruit that was considered a failure. It transformed him into a serpentine dragon which allows him to seemingly fly, when in actuality he somehow produced clouds that he was able to grab onto and climbed up that way.
However, as he has only eaten this fruit recently, he does not seem to have much control over it yet, and in fact transformed unwillingly into his full animal form shortly after consuming the fruit. He did not know that he could produce and climb clouds, as he told Luffy he was stuck in the garbage dump when they met there. When he was frightened by a hunger-induced hallucination, he unconsciously used his cloud ability to escape with Luffy clinging to him. He also did not know he could switch forms until Luffy told him. It is also possible, though, that he has no conscious control over his power because the fruit was artificial and a failure. He showed the ability to revert back to his human form when he reunited with his father, Kin'emon. However, Momonosuke is shown to switch forms from time to time. Momonosuke, alongside Kin'emon, Kanjuro and Raizo were heading to Zou, but ended up shipwrecked, in which they got separated from Raizo, and drifted ashore to Dressrosa. While in the country, Momonosuke witnessed Doflamingo's brutality as he tortured one of his subordinates for showing weakness. The samurai were later pursued by Doflamingo's men. Momonosuke hid himself in a ship and the ship set sail before his father could reach him. Momonosuke was taken to Punk Hazard where he was placed in the Biscuits Room with the rest of the children. Despite the other children's kindness to him by offering him food and candy, he refused to take "another's charity" and told no one his name. Sometime after sneaking out of the Biscuits Room, he wandered into a "secret room," which in reality was Vegapunk's former office. There, he saw the scientist's man-made Devil Fruit inside of a glass display case. Due to his hunger, he smashed open the case and ate the fruit. Soon after, a little girl found him inside the room and talked to him upon entering. Momonosuke told her that he needed to escape and that he had something he needed to accomplish. He listened to her as she talked until they heard the guards coming. She ran away to hide after telling Momonosuke to do the same. By the time the guards got there, Momonosuke underwent an unconscious transformation into his dragon form. After escaping the guards, he saw his reflection and, upon realizing that he was the dragon, screamed in shock and continued to run away. Running past Caesar Clown's office, Momonosuke overheard the deranged scientist talking about the newest batch of children and how they were only good for about five years of experiments, after which they would die. He was going to warn the other children, but he thought to wait in the garbage dump where he ended up becoming trapped.