Hot-blooded and fiery, Han Tae Eun is well known in her school as a formidable fighter, more inclined to her fists than talking things through. She yells often, especially at Sa Ghang Gwon when he aggravates her. As a child her mother was killed by a Trouble in a park, and Tae Eun repeatedly visited the same spot her mother died, until she found a barely-conscious Sa Ghang Gwon lying there. She took him home and adopted him as her possession. At some point in time, she discovered he was a Trace and labored to protect his identity, unbeknownst to him.
When Sa Ghang Gwon is taken away by the government, Han Tae Eun declares that she will become a Trace and be like him. She repeatedly battles Troubles at the expense of her own life, but then she awakens as a Trace. Her arms turn a sparkling red and shoot sparks, granting her inhuman strength and abilities. It seems that she needs to repeatedly punch hard objects like the ground to activate one of her arms, but if she strikes her fists together, the other arm will ignite.
Tae Eun is easily angered and irritable but also fiercely protective of Sa Ghang Gwon. She protects him specifically to prevent him from fighting back, so that he won't accidentally reveal his identity as a Trace. She seemed to resent that he was a Trace while she wasn't and accused Ghang Gwon of the same feelings, since he tried to hide his true identity from her. She's stubborn, believing that if she fought Troubles, she would become a Trace. After she becomes one, she goes about fighting Troubles, in the same way Ghang Gwon did (dressed with a face mask). Tae Eun seems to hold romantic feelings for Ghang Gwon, getting jealous when he carries Se Yeon and tells Tae Eun to run while escaping a Trouble.