Sa Ghang-gwon

is a Trace with the ability to manipulate ice. His powers had been with him since his birth, and because he could not control them, Ghang Gwon accidentally attacked his own parents. With no cure or solution to Traces, his parents abandoned him on a street next to an old beggar woman Trace who could conjure fire. He wandered around for an indeterminable amount of time, living his life as a scavenger and losing his emotions. He engaged in battle with his first Trouble, but after realizing he could not defeat it, he encased himself in ice until it disappeared. He passed out in a park, where he was found by Han Tae-eun. She took him home and asked her father if she could keep him. Afterward Tae Eun called Ghang Gwon her possession. Her family, consisting of only her and her father, adopted him, but Ghang Gwon, fearing that they would abandon him like his parents, hid from them his identity as a Trace. Over the years, he continued to battle Troubles, honing his skills. Whenever he is injured, though, he lets Tae Eun believe that he was bullied by his classmates.

When a Trouble attacks his class, Ghang Gwon attempts to come to the rescue, but Tae Eun stops him, knowing that if he fights the Trouble, his identity as a Trace will be revealed. She begs him not to get involved, but Ghang Gwon engages the Trouble and defeats it. Afterwards, he is taken by the government for three months, and then enrolled in a Trace school. His prime objective is to leave the Trace school and return to his family as soon as possible, and he believes that capturing the Beggar Team will grant him freedom.

Ghang Gwon is very quiet and almost antisocial. He hates that he is a Trace, shamefully hiding it from Han Tae Eun and her father; oftentimes, he mutters to himself that he is not a Trace. But he also specifically uses his powers to battle and destroy Troubles, so that his family can be safe. He is easily bullied and also submits to their beatings without complaint (for the sake of Han Tae Eun's safety), which only angers her. He has no facial expressions and seems to enjoy antagonizing her, calling her "battle addict" or "fighting chicken." He is extremely protective of her and her father, as his family. He seems to find Tae Eun especially precious. It is hinted that he likes her as more than a sister; while in the Trace academy, he repeatedly writes letters to her, ending each with the words "I miss you."

Trivia
In the Japanese version of Trace he's called "Yuu".