Jinbei first appears as a villainous pirate in the One Piece series, as a part of the powerful crew of Arlong. Over time, however, his true identity comes to light; Jinbei is actually a highly respected fishman, and a capable swimmer who is respected by the Fishman Island. It is eventually revealed that Jinbei had originally been a member of the Neptune Army, and that his mission to join the Arlong Pirates was to destroy the threat of piracy in the East Blue.
He later joins the Straw Hat Pirates, and his role in their crew has evolved significantly over time. Initially, he was seen as something of a mascot for the crew, providing comic relief and often using his skills as a swimmer to help Luffy and the others out of sticky situations. As the series has progressed, however, Jinbei has become a powerful warrior, combining martial arts and fishman karate to great effect.
Jinbei officially joined the Straw Hat Pirates following the events of the Fishman Island arc. After standing up to Hody Jones, the leader of the New Fishmen Pirates, Jinbei demonstrated his loyalty and devotion to the Straw Hat crew. Luffy was so impressed with his courage and bravery that he officially invited him to join the crew, to which Jinbei eagerly accepted.
Since then, Jinbei has become a powerful member of the Straw Hat Pirates’ crew, relying on his aquatic skills to help the others on their adventures. In addition to his tremendous strength, Jinbei has also enhanced the crew’s strategic capabilities as a result of his vast knowledge and understanding of the ocean and its creature. Luffy often refers to him as his “Water Master” for this reason.
Jinbei’s skills have been especially useful on their travels around the New World, and he has often been the one to dive into the depths of the ocean to search for rare and mysterious artifacts, as well as helping to capture powerful sea monsters. On top of this, Jinbei is also an invaluable member of the crew as a result of his willingness to defend his crewmates to the death.
Overall, it can be said that Jinbei’s decision to join the Straw Hat Pirates has been one of the most beneficial choices he has made in his entire life. The powerful and kindhearted fishman has quickly become an irreplaceable and beloved member of the Grand Line, and his skills and loyalty will no doubt continue to prove invaluable on the crew’s ongoing adventures.