Kokoro is the main conductor of Tom's Puffing sea train, at the outdoor station of Water 7 and the icefish mermaid. He had a grandson named Chimney, who often accompanied him everywhere. He is Tom's former secretary.
Appearance
His facial features make him look as if he is constantly smiling regardless of his true emotions. The shape of his body, together with his strange smile, made him look like a frog. He is, in fact an icefish mermaid, although he is more like a dugong in terms of appearance and shape.
Personality
Kokoro is a heavy drinker, and speaks in a light tone that gives his dialogue a distinctive ring. While he does not have an angry attitude, he tends to remain under control and seems to be always happy no matter what happens what happens to be relaxed and calm.
He liked the figure of Luffy, a young captain and finally referred to him as the Pirate King. He was very curious about him because the events at Enies Lobby were very interesting. He came to the conclusion that if Tom was still alive, he would build himself a ship like he had done for Gol D. Roger.
Like many other characters he has a unique laugh with "Nga" (Nga..anganganga).
Ability and Strength
Kokoro is an experienced train marine conductor who is adept at operating the vehicle. Thanks to his expertise, the alliance between the Straw Hats, Galley-La foreman, and the Franky Family was able to reach Enies Lobby after pursuing Tom's Puffing using Rocketman. His expertise was also noted where he could see the track even during the worst storm and successfully land Rocketman on the tracks. His status as a mermaid also proved useful for the Straw Hats, saving them from drowning due to the floodwaves created by Rob Lucci.
He only shows one attack named; "Mermaid Kick" (? マ ー メ ド キ ッ ク, Māmeido Kikku?), With which he kicks opponents with his fish tail fin with a strength strong enough to send marines flying away. He is a fast swimmer, like all other mermaids.
History
Past
Early life
He left Gyojin Island to support Tom and met his human husband in Water 7. Together they had a son who was half a half-mermaid.
Secretary Tom
When Tom was brought to court in 1500, Kokoro witnessed everything. After Tom was given a ten-year sentence for building a sea train (extended to fourteen years later), Tom only laughed about being given a chance, but Kokoro was afraid of Tom's attitude about his sentence, and didn't appreciate him laughing about it.
At some point over the next fourteen years, Kokoro visited Enies Lobby with Tom, and memorized several locations for future reference.
When the sentence was almost complete, the judge, impressed with Tom's work, intended to forgive him. However, the director of CP5Spandam was troubled by the verdict and then attacked the judicial ship on Franky's Battle Franky, thus cornering Worker Tom. Kokoro tried to stop Franky from making matters worse by fighting back.
When Tom is captured by Spandam and his agents, Iceburg, Franky, Kokoro and Yokozuna are brought to court. To save Iceburg and Franky, Tom sacrifices himself by saying that he is proud to help Gol D. Roger, and hurt Spandam. After Tom was appeased, the Judge decided to take only Tom and release the workers. Kokoro hugs Franky and Iceburg as he explains that inmates have never returned from Enies Lobby. Annoyed, Franky attacks Spandam with a rifle butt stolen from the marines and causes permanent damage to his face. After Franky was hit by a sea train, Kokoro told Iceburg that Franky was dead.
Source : WIKIA ONE PIECE