Related stories:
Qiao Ba's first appearance was when he and Dr. Kuleiha went to Kester Town on Cigu Island to look for patients. Later, he came into contact with straw hat pirates for the first time because he helped treat Nami who was infected with the virus and Luffy and Shan Zhi who were seriously injured.
When talking with Nami who recovered from illness, Qiao Ba showed his yearning for pirates, so Nami invited him to join as a doctor, but he shirked it on the grounds that he was a reindeer and could not be with humans.
Extended data
Related background:
After defeating Wapol, Luffy invited Qiao Ba to join as a partner for many times, but Qiao Ba was always in a state of war. He repeatedly thought that he was a reindeer, so he was not qualified to join.
After a whole day of "invitation" and "escape", Luffy shouted at the top of his lungs to Qiao Ba, "Stop nagging and come with us", which not only washed away Qiao Ba's hesitation, but also gave him the courage to go to sea. After thanking Dr. Kuleiha, Qiao Ba left the Straw Hat Pirates and officially became their sixth partner.
Qiao Ba is determined to be a panacea for all diseases. As a doctor, I will never save an injured person from destruction. When I meet a stranger, I am afraid. In order to avoid strangers' eyes, I hide behind obstacles, but I often just hide my head and show my body.
Baidu Encyclopedia-One Piece