Not much is known about what they do in Kano Country, but the two members seem to be very loyal to their leader and grandfather, Don Chinjao.
Members of the family have a blood relationship with each other. Sai and Boo are the grandsons of Don Chinjao who is the head of Chinjao Family. All three of them are (or in Chinjao's case, was) in the Happo Navy, and specialize in the Hasshoken (八衝拳 Hasshō-ken?, literally meaning "Eight Impacts Fist"), a fighting style that imbues vibrations in a strike to break the enemy's armor and weapons, similar to Whitebeard's Gura Gura no Mi.
In the past, their leader was a fearsome pirate, worth over 500,000,000. After Monkey D. Garp dented Chinjao's pointed head, robbing him of his power and the means to acquire his fortune, Chinjao swore to get revenge on Garp and his family.
During the Dressrosa Saga the group traversed to Dressrosa, ostensibly to compete at the Corrida Colosseum for the Mera Mera no Mi. Their true purpose, under orders from the king of the Kano Country, was to investigate and cripple a weapons trade that the Donquixote Family managed, whereby Doflamingo sold weapons to warring nations, including those opposing the Kano Country.
After they arrived and signed up, all three were placed in C Block. Later, during B Block, Chinjao met with Monkey D. Luffy, the grandson of Monkey D. Garp, who was also competing in C Block. He attempted to kill Luffy before the match, but Sai and Boo stopped him. Chinjao planned to kill Luffy during C Block.
During the battle royale, Boo was defeated by the Funk Brothers and Sai was later knocked out of the ring by Luffy. Chinjao and Luffy then became the last two contestants during this round. After a fierce battle, Luffy overpowered Chinjao but also inadvertently restored his pointed head.
After the match, Chinjao was appeased and he ceased his desire to kill Luffy. Sometime later, they were tricked and thrown into an underground dungeon along with the other disqualified participants. Sai and Boo were soon abducted and transformed into toys while Chinjao lost all memories of them.
Sometime later, Chinjao was turned into a toy as well and the Chinjao Family was forced to work as slaves in the underground trade port. When Sugar lost consciousness, her curse broke and the Chinjao Family returned to being humans again.
During the battle to overthrow the Donquixote Family after Doflamingo initiated his Birdcage plan, Boo fought and was defeated by Machvise while Chinjao engaged Lao G in battle and Sai was fighting with Baby 5. As Sai fought with Baby 5, she misunderstood his threats as flirting, which greatly confused Sai. Later on, Chinjao became distracted from his fight with Lao G and told Sai that he was against his union with Baby 5, but his grandson retorted that he was not going to marry. Baby 5 then asked Sai how she could be of use to Sai, which he sarcastically said he wanted her to kill herself. Baby 5, taking him seriously attempted to kill herself, thinking she could be useful. Sai attempted to stop her, which infuriated Chinjao, because he detested saving enemies. He went to attack Sai with Drill Nail, but Sai countered with Bujaogen, which bent Chinjao's drill head. After this, Chinjao realized Sai had awoken his power. He bestowed the Hasshouken Secret Technique: Drill Dragon to Sai and gave him full power over the Happo Navy. Chinjao was about to tell Sai how proud he was of him before a much larger Lao G attacked him and knocked him into a wall, defeating the old pirate. Lao G then set his sights on Sai, calling him "a monkey from the Kano Country" and told him he could not have Baby 5 while referring to her as "convenient", hurting her feelings. In response to his grandfather's defeat and Baby 5's honor, Sai retorted that if he won he would marry Baby 5. Sai then used the Hasshouken Secret Technique: Drill Dragon Nail for the first time and with it, he defeated Lao G whilst shattering the ground.
When Doflamingo started shrinking the Birdcage, Mansherry temporarily healed the injured. The Chinjao Family and the other gladiators defeated the remaining Donquixote Pirates on the New King's Plateau to help the citizens flee from the shrinking Birdcage. When the Birdcage came close to the central streets, the gladiators work together to push back the Birdcage via Bartolomeo's barrier. Once Luffy finally defeated Doflamingo, the gladiators witnessed the collapse of the Birdcage. Later that night in the aftermath, the Chinjao Family and the other gladiators rested at the palace.
Three days after Doflamingo's defeat, the Chinjao Family and the other gladiators prepared to assist the Straw Hats' escape from Dressrosa when the Marines were mobilized to pursue them. After escaping from Dressrosa, Sai was among the seven leading representatives to swear allegiance to the Straw Hats as gratitude for their role in saving them from being slaves under the Shichibukai. Though Luffy declined their offer, Sai swore his loyalty anyway, becoming the leader of the third division of the Straw Hat Grand Fleet. After a celebration, Sai took a piece of Luffy's Vivre Card before parting ways with Luffy.
The Stories of the Self-Proclaimed Straw Hat Grand FleetEdit
After parting ways with the Straw Hats, the Chinjao Family journeyed back to their home country. Sai later spoke to Uholisia and broke off his engagement with her. Furious, Uholisia gave Sai a beating while her father scolded Chinjao. Sai and Baby 5 later had their wedding ceremony.