One element that makes One Piece such a dynamic world is that all the side characters still live out their lives when the Straw Hat Pirates aren't around. They have stories of their own that develop and change. Then, they often return to the story at a later date to show how they've been affected by their lives. Hatchan, nicknamed Hachi, is one of these characters. His introduction sees him as one of Arlong's lackeys.
His admiration for Fisher Tiger and his willingness to fight are a huge part of what led him to follow Arlong. Yet, the most radical part of his character development doesn't show up in the anime at all. He's forced to confront himself when he isn't following anyone during the "Hatchan's Sea Floor Stroll" cover series.
When Nami and the Straw Hats end up meeting him again, he's wildly different. Now, Hachi wants to prevent future generations from suffering Arlong's hate, the hatred that he helped propagate during his time with his last crew. Fisher Tiger wanted to free fish men slaves and prevent humanity from oppressing his people above all else. He also freed human slaves during that mission, notably the Hancock sisters and Koala. However, he had no love for humanity.
That being said, he was still willing to be kind to humans. He helped Koala overcome the traumas of being a slave. He didn't believe that fish men should integrate with humanity, but he also tried to ensure his crew didn't harm humans. Hachi was happy to be a member of the Sun Pirates and carry out these beliefs. After Fisher Tiger's death, the Sun Pirates broke up.
Arlong was enraged and further radicalized, and his attempts to avenge Fisher Tiger led to Arlong being arrested. He let Arlong free in this deal, but Arlong took the angrier members of the crew with him on a quest to punish humanity for everything they had done to fish men.
