When does Chopper join the crew?

In a flashback, Hiriluk determined to perform a miracle that would save the country by making cherry blossoms bloom in the Drum Kingdom. Despite Kureha's skepticism, Hiriluk was convinced that the vision would save his people, just as he was sure they had saved him years ago.

The flashback ended with Chopper reflecting on his time spent with Dr. Kureha and pondering his Jolly Roger while sitting on top of the Drum Castle after Luffy's battle with Wapol had concluded. He also recalls Hiriluk encouraging him once to go out to sea so that he could realize how little his concerns are. Following this, Luffy started chasing Chopper and insisted he should join his crew.

Dr. Kureha gathers the hurt Dalton, Sanji, and Nami and tends to them. She then requests the key to the castle armory from Dalton. He claims that Wapol would have had the key and that it most likely flew away with him. Nami intervenes, eager to discuss the terms of payment. Kureha agrees to forego payment in return for the armory key that Nami stole from Wapol during their confrontation.

Chopper decides against being a pirate after successfully hiding from Luffy. While Zoro and Usopp are certain that Chopper does not want to join them, Luffy continues to look for him. In truth, Chopper wanted to be a part of their crew but felt unworthy. As Sanji is being dragged out of the castle by Nami and Vivi, Chopper finally confronts Luffy.

Chopper tries to explain that despite his desire to be a pirate, he cannot join Luffy's crew because he is a reindeer, blue-nosed, and a monster. Ignoring whatever he says, Luffy screams at Chopper to stop talking and come with him anyway. Chopper bursts into tears as he realized he finally found friends who don’t see him as a monster.

Chopper gets some time to say farewell before leaving the island with his new crew. Kureha is supervising the men transporting the cannons outside the armory. When Chopper finds her, he lets her know he is leaving to take over as the Straw Hat Pirates' doctor. She chastises him, saying he doesn't appreciate her or her training and forbids him from leaving. Chopper runs away from her as Kureha chases after him.

As Chopper escapes the palace, Kureha cries to him, "You're chasing a lunatic fantasy, just like Hiriluk!". Chopper believes she is wrong because Hiriluk finished his research before he died. He arrives just as Usopp completes setting up the ropeway and shouts for the Straw Hats to board the sleigh. Dalton joins her while Kureha observes from the top of the ropeway. She claims that her pet just left, but she hates saying goodbye and then asks Dalton to meet her by the cannons when they are ready so she may send Chopper off.

Chopper wonders if Hiriluk ever finished his research or if he was simply lying to make Chopper feel better toward the end of his life. The cannons are fired outside Drum Castle, leaving the villagers wondering if the battle has resumed. Chopper comes to a halt and witnesses something extraordinary and it is then revealed, viaI a flashback, that Hiriluk had explained that the dust he had created would tint the snow pink. When it is fired from above, the mountain appears to be a massive cherry blossom tree, and the snowflakes resemble dropping cherry blossom petals. Chopper cries when he sees the results of his father figure's work and the episode ends as Kureha bids Chopper a final farewell.

1. Chopper became a member of the infamous Straw Hats Pirates crew.
2. As Drum Island gets covered in cherry blossoms, Hiriluk’s research finally comes to fruition, leaving Chopper and everyone on the island moved by it.

Q. When did Chopper join the Straw Hat Pirates in the manga?

A. Chopper joined the Straw Hats Pirates as their crew’s doctor in chapter 153 of the One Piece manga, titled “Hiriluk’s Sakura”.

Q. What are Chopper’s devil fruit powers?

A. Chopper ate the Hito-Hito no Mi, also known as the Human-Human fruit, a Zoan-type devil fruit. This gave chopper the ability to transform into a human/human hybrid at will, making him a Human Reindeer.