One night, Choi was standing in front of his butcher shop, contemplating the stars. Once again, the need for some action in his life invaded his mind. And as of fate would have wanted it, a huge, bulky man came running into Choi. After a few minutes of recoil, Choi was astonished at the giant individual. He was fat, bald, bearded, and wielding a huge iron ball. It was Chang Koehan, the infamous criminal, who had just broke out of jail. Soon, Chang told Choi about all the fun and excitement in his crime life, and Choi got excited all of a sudden. Seeing Choi's gleer, Chang decided to invite him as a partner at night. Choi soon took out his steel claws which he had built himself, and began his adventures with Chang, without his wife ever knowing.

Chang and Choi thrived in terrorizing the local population with their evildoings. Mugging is the best thing that they practiced. Choi now led a double life: pacific butcher man by day, little terror by night. He finally found himself alive by seeing the face of horror of his victims. That is, until he came...

In a cold night, Chang and Choi had located their latest targets, one of them being a young woman. As soon as the duo prepared for the assault, a sudden white streak cruised their eyes. Quickly and efficiently, Chang and Choi were sent flying into the air. Having a hard time recovering, Chang and Choi barely distinguished a man in a white "dogi" (uniform). It was the fighter of justice, Kim Kaphwan! Kim had already heard about them, and decided to rid the world of the evil scum, he decides to reform the two criminals by taking them to his dojo and training them on Tae Kwon Do. Choi opposed instantly, but he was swiftly whacked by Kim (and Chang, too, even though he was just looking!).

Thus, began the personal hell of Chang and Choi. Choi was promptly "retired" from his night criminal life, and had to train instead. Choi soon regretted the day he desired having emotions in his life, since all that it led him to was a lifetime of training under the sadistic Kim. Day after day, Chang and Choi planned their escape, but failed miserably each time (and gaining a subsequent beating afterwards). Choi saw the liberty a few feet away a few times, but Chang always screwed up. However, Choi never loses hopes to run away from Kim and finally go back in business!

During a normal, hard training day with Kim, Choi met a man that had trained aside Kim long ago, but was totally different from him: he was ruthless, and quite a short-tempered fellow. Choi saw in him a last chance in escaping from the clutches of the merciless Kim, but it would soon turn out totally against him: the man, Jhun Hoon, was there to show the TRUE ways of justice: the way of violence! The cavalry continues for Choi, and more so when, just after the 1999 version of the King of Fighters tournament, he is assigned to the same Jhun to see which method of training is best. It seems that there will be no way in hell that the criminal duo will be escaping soon!

Upon training during a very long year with Jhun, Choi gets more and more hopeless about escaping one day, since Jhun has made it clear that he and Chang are going to be around for a long time if they don't make amends! When Chang and Choi finally get reunited for the King of Fighters 2000 tournament, Chang proposes Choi to do his best to destroy the NESTS cartel in order to give Kim and Jhun a good impression. Choi thinks it's a good idea, and that he will do his best in order to be free once and for all!

Destiny plays a cruel card, however, when Choi finally reaches Southtown in time for the finals. He and Chang arrive just in time of the Zero Cannon explosion...Choi and Chang are the only persons who don't escape at time from the inminent blast. Kim and Jhun manage to rescue the two ex-convicts, but when Choi and Chang finally wake up, the realize in panic that they have changed bodies! Now it seems that they will be attached with Kim and Jhun for awhile until they manage to find a solution, even if it means going up to ask NESTS for a favor.

Choi was living a pure hell living in Chang's gigantic body, not being able to move as quickly as before. But Kim had the perfect solution for this exceptional case: Chang and Choi should butt heads repeatedly until they switched back again! Much to Choi's surprise, the plan actually did work, and he happily returns to his midget self, only to know that he must train once again for the next King of Fighters tournament. Another year of suffering seems to loom in the horizon, but Choi's take on life changes when Jhun is wounded in a street accident. This leaves the team short one member, and Choi considers this the chance to finally rest one year of the King of Fighters tournament. But Kim had a backup plan, which involved recruiting a new member, straight from his dojo.

Choi cringed at the idea of yet another Kim wannabe in his team, but the student that Kim referred to was no other than a young woman called May Lee. She shared the same justice principles than Kim and Jhun, but she wasn't even half as cruel or psychotic. Choi was surprised that some student of Tae Kwon Do could actually be tolerant with him and Chang! Aside from Kim's strict discipline, Choi sees in May Lee a chance to actually have fun in the tournament. Choi puts his best effort in the tournament, and the result is the ultimate destruction of NESTS. Choi and the others are received as heroes in their native Korea, even though they weren't the main stars of their downfall. In the celebration parade, Kim and Jhun get in an arguement about who is the true hero of the story. But Choi and Chang know better: they couldn't have done it without the help of May Lee, as Choi claims with pride and joy!

Choi is always taking advantage of the opportunity to show off and impress Kim, and see if that way he can finally gain his liberty. He is the best of friends with Chang, but he truly hates that Chang always says the wrong things in the wrong times! Choi always loves the excitement of battle, and loves to gouge claws into the opponents' flesh.