The Fast and the Furious: Tokyo Drift

This film's story occurs sometime after Fast &amp; Furious 6 with a scene that was later made concurrent with events in Furious 7.
In Oro Valley, Arizona, 17-year-old high school students Sean Boswell (Lucas Black) and Clay (Zachery Ty Bryan) race their cars to win the affections of Clay's girlfriend Cindy (Nikki Griffin). When Sean cuts through a structure and catches up to Clay, Clay hits Sean's car repeatedly until they reach a high-speed turn, which causes both cars to crash; Sean's car is totaled. Clay's wealthy family helps him escape punishment, but Sean is sent to live in Tokyo, Japan, with his father, a U.S. Navy officer, in order to avoid juvie or even jail.
While in school, Sean befriends Twinkie (Bow Wow), a military brat who introduces him to the world of drift racing in Japan. Sean has a confrontation with Takashi (Brian Tee)âaka D.K. (Drift King)âover Sean talking to Takashi's girlfriend Neela (Nathalie Kelley). Though forbidden to drive, Sean decides to race against Takashi, who has ties to the Yakuza. He borrows a Nissan Silvia from Han Seoul-Oh (Sung Kang), now a business partner to Takashi, and loses, totaling the car because of his lack of knowledge of drifting â racing that involves dangerous hairpin turns.
To repay his debt for the car he destroyed, Sean must work for Han. Later on, Han becomes friends with Sean and teaches the young racer how to drift. He also loans him another car for future races. Han explains that he is helping him because he is the only person willing to stand up to Takashi. Sean moves in with Han and soon masters drifting, gaining some repute after defeating DK's right-hand man, Morimoto. Sean soon asks Neela out on a date, and learns that after her mother died she moved in with Takashi's grandmother, resulting in her hooking up with him. Takashi beats up Sean the next day, telling him to stay away from Neela; Neela subsequently leaves Takashi and moves in with Sean and Han.
Takashi's uncle Kamata (Sonny Chiba) (the head of the Yakuza) reprimands Takashi for allowing Han to steal from him. Takashi and Morimoto confront Han, Sean, and Neela about the thefts. Twinkie causes a distraction, allowing Han, Sean, and Neela to flee, pursued by Takashi and Morimoto. During the chase, Morimoto is killed in a crash, leaving Takashi to pursue Han, Sean, and Neela on his own. Han allows Sean to overtake him in order to hold him off, but the chase ends when Sean and Neela crash. Meanwhile, moments after escaping from Takashi, Han is critically injured when his Veilside Mazda RX-7 is rammed by an oncoming car that catches on fire, and explodes; the explosion kills Han just seconds before Sean has a chance to save him.
Takashi, Sean, and his father become involved in an armed standoff which is resolved by Neela agreeing to leave with Takashi. Twinkie gives his money to Sean to replace the money Han stole, which Sean then returns to Kamata. Sean proposes a race against Takashi to determine who must leave Tokyo. Sean and Han's friends then build a Ford Mustang '67, with a Skyline GT-R RB26DETT engine salvaged from Han's Nissan Silvia, and other spare parts.
That night, on the mountain, crowds gather to see the race; Takashi takes the lead initially, but Sean's training allows him to catch up. Determined to win, Takashi resorts to ramming Sean's car, eventually missing and driving off the mountain while Sean crosses the finish line. Kamata keeps his word and lets Sean remain in Tokyo (In a deleted scene, Kamata has Takashi taken away).
The next night, Sean, the new "Drift King," is challenged by a new driver who claimed Han as family: Dominic Toretto (Vin Diesel). Having heard of Dom's reputation, Sean says "you know this ain't no 10 second race," in which Dom responds; "I got nothin but time."

Question: Who does Sean have to work with to repay his debts?
Answer: Han