Kawamatsu the Kappa is a Japanese puffer fish-man who is a yokozuna-ranked sumo wrestler. As a child, he was shipwrecked in Wano and orphaned soon afterwards. After Kozuki Oden rescued him from citizens ostracizing him, he went on to serve as one of Oden's Nine Red Scabbards until Oden's death 20 years ago. Kawamatsu would go on to be imprisoned by the Beasts Pirates for 13 years until he was ultimately freed by Monkey D. Luffy, and he reunited with the Nine Red Scabbards to fight Kurozumi Orochi and Kaido and avenge Oden. Kawamatsu is a large Japanese puffer fish-man whose appearance could be mistaken with that of a kappa. As such, he has webbed hands and green skin. Being almost as tall as Raizo at 271 cm, he has a round body, two blush marks on his cheeks, a beak-like mouth and extremely long and wild orange hair. He wears a green kimono, a red cape, sandals, and a large kasa with a dark diamond shape at its top. Kawamatsu is an extremely kind and caring person, as shown by his care for Kozuki Hiyori and his efforts to make her laugh after the trauma she went through. When one of the Beasts Pirates attempted to attack Luffy, Kawamatsu silently aided him by attacking his attacker with a fishbone. His compassion is best shown when he encountered an impoverished Onimaru and fed him with his limited amount of food, despite there being barely enough for himself. Due to his mother insisting that he plays a kappa in order to protect himself from the Wano Country citizens, he takes the role quite seriously, never introducing himself as a fish-man but as a kappa.
Kawamatsu appeared to be very close to his mother, as she protected him from discrimination until one event led to her demise. In her dying moments, she told her son to act as a kappa for better survival. To honor his mother, Kawamatsu obediently heeded her last words for many years and has continued to refer to himself as a kappa in the present. He even named his personal swordsmanship style after it. Kawamatsu was extremely grateful to reunite with Raizo, shocked that he hadn't aged a day. Like the other Scabbards, he was shocked by Kanjuro's betrayal. As a small child, Oden saved Kawamatsu from death by discriminatory humans and offered him freshly cooked food, which Kawamatsu was extremely grateful for. From then on, Kawamatsu became one of Oden's most loyal followers. His trust in Oden is such that he revealed his heritage as a fish-man to him despite his mother's dying words for him to hide it to protect himself from persecution. In turn, Oden entrusted Kawamatsu, along with the other retainers, with his dream to open the borders of Wano Country. As Oden's retainer, Kawamatsu is also extremely loyal to his lord's children. He was the one who helped young Hiyori escape from their enemies at Oden Castle and took care of her for 7 years during her childhood, even endured long term starvation to ensure Hiyori had enough food, making Hiyori chose to ran away out of concern for him. When she ran away, Kawamatsu desperately searched for her and was filled with regret when he could not find her. After reuniting with Raizo after twenty years, the first thing he did was asking about Momonosuke's safety, showing his concern for Oden's son. Unlike Ashura Doji (who refused at first), Kawamatsu had been eager to join the Kozuki Family in the war against Orochi and Kaido. When reuniting with Hiyori after many years, they were extremely overjoyed to see each other again. He also tried to rescue Momonosuke when the latter was captured by Kanjuro and he was enraged when Kanjuro declared that he will hunt down Hiyori. In his youth, Kawamatsu tried to steal money from Yasuie along with the Nine Red Scabbards only to get caught. Yasuie held no grudge against him and his retainer comrades. Instead, he convinced them to behave as real retainers to support their lord Oden and Wano while freely giving them the money. When Orochi killed his benefactor, he grieved for his death as he watched his execution. Kawamatsu first met Onimaru 13 years ago, who chased some members of the Beasts Pirates. Kawamatsu nursed the wounded komakitsune back to health. At first, Onimaru was hostile towards Kawamatsu, refusing to let the samurai collect the weapons of the buried in Ringo but he relented when Kawamatsu offered him his arm. He and Onimaru then worked together to protect the graves from robbers.
However, less than a year later, Kawamatsu was captured and Onimaru inherited the name "Gyukimaru". In the present day, when Kawamatsu interfered in "Gyukimaru" and Zoro's battle, Onimaru expresses tears of joy upon learning that Kawamatsu is still alive. As a member of the Nine Red Scabbards, Kawamatsu is a powerful samurai whom Kin'emon states (alongside Denjiro and Ashura Doji) is worth 100 men in battle. As a fish-man, Kawamatsu is a fast digger and swimmer, which enabled him to sneak Hiyori out of Oden Castle. Kawamatsu possesses tremendous physical strength as he is stated to be the strongest sumo wrestler in Wano. Shortly after being released, Kawamatsu overpowered multiple members of the Beast Pirates with great ease. Alongside his fellow Scabbards, Kawamatsu managed to push Kaido off his feet when ambushing him. Kawamatsu possesses immense endurance as he has been fed poisoned fish every day for thirteen years by the Beasts Pirates without dying or even suffering any illness like Tama, a feat which has baffled his captors. However, it has been shown later on that Kawamatsu had to throw up once he was freed. He was also shown to go on providing for Hiyori while starving himself. He could withstand Onimaru violently biting his arm and survive the freezing cold winter climate of Ringo as well as days of hunger. Kawamatsu is capable of spitting projectiles with great speed and precision, potentially turning them into deadly weapons if they are sharp enough. He was able to take out a guard by using a bone as a projectile that pierced his neck. Kawamatsu is an extremely skilled and powerful swordsman. He wields a shirasaya named Soto Muso and prefers fighting using a reverse grip. Raizo states that his skill has not waned at all after thirteen years of imprisonment. He calls his personal style the Kappa-ryu, which is a Strong Blade swordsmanship incorporating his powerful fish-man strength and sumo skills to create rushing attacks that can overpower large numbers of opponents with sheer force. Kawamatsu is a master of Busoshoku Haki, which is known as "Ryuo" in Wano. His skill is shown when he performed an attack named Yagura Ryuo, literally meaning "Tower Flowing Sakura") which repelled several Beasts Pirates charging toward him without direct contact. When fueled by rage, he is able to pierce through Kaido’s tough skin with his Haki-infused sword.
