Quantum Mistake (originally titled Change Guy) is a manhwa published in 31 volumes between 1998 and 2006. It was written by Son Eun-ho and illustrated by Choi Myung-su. It tells the tale of two boys, Woo-Soo Choi and Kang Too-Jee, whose souls are accidentally switched.

On the day a scientist is performing body-teleportation experiments, Woo-Soo Choi and Kang Too-Jee get into a fight after Woo-Soo accidentally pulls down Kang Too-Jee's trousers. As they fight, the scientist—who had been chasing a homeless person she had tried to bribe—runs them over and uses them to test her new teleportation device. The teleportation appears successful; she dumps their bodies and drives off, only to discover the device malfunctioned. She had teleported their bodies but not their minds.

When Woo-Soo wakes up, he sees his own body lying on the ground. Realizing their minds have been switched, he carries the unconscious body to the hospital. When Kang Too-Jee, now in Woo-Soo's body, wakes up, he seems to have amnesia and has reverted to a childlike state. Woo-Soo's mother believes the boy in Kang Too-Jee's body caused the incident and chases him out of the hospital. Woo-Soo Choi is able to find out where Kang Too-Jee lives and goes to school, but soon trouble appears in the form of Kang Too-Jee's old rivals and the fighting begins.

Characters

Woo-Soo Choi: Currently inhabits Kang Too-Jee's body. Extremely studious with exceptional concentration, he has a very kind heart but is often misunderstood because of Kang Too-Jee's personality and past. He becomes a student of the Gyuk Moo-Do martial arts school in order to fight one of his first enemies.

Kang Too-Jee: Currently inhabits Woo-Soo Choi's body. Initially suffering from amnesia, he is not seen often until later volumes. He recovers his memory during a fight and confronts Woo-Soo Choi. Afterward, he stays at Woo-Soo Choi's house at Woo-Soo's request so his mother will not be upset. He becomes a Judo student—a discipline he could never previously master but can now because Woo-Soo Choi's body is weak yet extremely flexible (double-jointed).

Park Yu-Na: Beautiful and popular among boys, she is afraid of gangsters and troublemakers. She always thought Kang Too-Jee was scary and violent until Woo-Soo Choi took over his body. She then begins falling for the person she believes is Too-Jee but who is actually Woo-Soo.

Do Do-He (also spelled Do Do-Hye or Do Do-Heh): Attractive, smart, and stubborn, she is Kang Too-Jee's landlord. She dislikes him until Woo-Soo Choi takes over his body.

Chun Moo-Jin: A long-haired, pretty-boy type of character. He befriends Kang Too-Jee when they learn Hapkido together. He very quickly becomes obsolete as a fighter but remains an amusing character. He is also in love with Do Do-He (Yun-Na's close friend).

Supporting characters — The Four Dragons of Goo-Ryong High School:

Ji Kang-Hyuk: The leader of the Four Heavenly Dragons, the Daeil Cheonhwang of Goo-Ryong High School. He is an incredibly gifted fighter who likes to chain together aerial moves. At the beginning of the story he is the strongest fighter in Seoul. He is defeated in volume 12 by Shin Jin-Ho. After the defeat he trains for a year and learns the Corkscrew Punch in an effort to redeem himself in a rematch. He then participates in the tournament against the five gang leaders from the correctional institute; his first opponent is the savage Mah Kang-Chul. He delivers the Corkscrew Punch countless times but is still defeated by Mah Kang-Chul. After the match he apologizes to Shin Jin-Ho for breaking their promise of not losing until they fought each other.

Pi Ho-Chul (boxing): The weakest of the Four Heavenly Dragons. A good-looking womanizer, he crosses paths with Woo So-Choi when he tries to hit on Yun-Na and Do Do-He. He is Japan's young amateur representative, and later, when he becomes a pro boxer, he runs for nomination for Rookie of the Year. Pi Ho-Chul is the first of the Four Dragons to face Woo So-Choi. Someone challenges him to a boxing match, thinking Woo So-Choi has the boxing abilities of the real Kang Too-Jee; he loses the match despite cheating. One year later he becomes a pro boxer and is easily defeated by Jegal Mih-Yang during the mainland hunt.

Jee Dae-Woong (Judo) is the second weakest of the Four Heavenly Dragons. He is a very tall, strong man and the captain of the judo club at Goo-Ryong High School. He is defeated by Han Sang-Jin during Han's revenge on the Four Dragons for destroying his Tae Kwon Do master. During the correctional institute tournament, he is quickly defeated by Kwon Shin's palm-twisting attack.

Dokko Dae-San (or Dokgo Dae-San) (Wrestling) is the one who defeated Han Sang-Jin's Tae Kwon Do master. He is the captain of the wrestling club and has great technique and strength (capable of bench pressing 300 kg). He never participates in a fight unless he has a 100% chance of winning. He defeats Han Sang-Jin in less than three minutes when the latter attempts to avenge his master. After Woo So-Choi's special underwater training, Woo So-Choi fights Dokko Dae-San and wins. A year later during the mainland hunt, Dokko Dae-San fights Jang-Suk Chung and loses badly; he ends up in the hospital with many bones broken, including his chin.

Han Sang-Jin (Tae Kwon Do) is a former member of the Four Heavenly Dragons. He joined only as part of a plan to exact revenge on the four dragons for what they did to his taekwondo instructor, Ryu Nam-Jin. A natural-born talent, Han Sang-Jin prefers real-life training and frequently participates in fights. His initial goal is to defeat the man who beat his instructor. He defeats Woo So-Choi, Jee Dae-Woong, and Pi Ho-Chul, but loses to Dokko Dae-San in under three minutes.