Jaekyung has short black hair, dark eyes, he's 26 and has a fairly pale complexion. He has Korean features (since he's Korean). He's 193cm tall and has a well-built body. He has two tribal tattoos, one on his left shoulder and one on his right arm. He can be caring(mostly only with Jieun). He's quite serious and calm even though he gets easily angry, but he likes teasing Jieun because he wants to see her cheeks red with embarrassment, usually when he's drunk he's more affectionate. He grew up in a VERY poor background, due to his father, Joo Jaewoong. Jaekyung's father was a former MMA fighter who fell into alcohol and drugs. After Jaekyung's birth, things got worse, so Jaekyung's mother decided to abandon both, her husband and son, to start a new life. Jaekyung was often beaten by his father and lived as best he could, sometimes stealing food, other times starving, until he met a man who started feeding him and invited him to visit his MMA gym. At first, Jaekyung was bullied by the other kids, but then he got stronger and continued training. Unfortunately, Jaekyung missed his mother very much, so one day he decided to call her, only to discover that she had started a new family and wanted nothing to do with him, so he doesn't know where is mother is. After his first major victory, Jaekyung rushed home to show it to his father, to show him that he did it, but found him unconscious, having overdosed. After his father's funeral, Jaekyung decided to leave the country and move to Seoul, but he kept having nightmares about his father and couldn't win any matches. He discovered his jinx: hooking up with someone the night before each match, which allowed Jaekyung to forget about the nightmares. Now he's a world champion; people call him Tyrant, The Emperor or the Undefeated Legend. He's rich and lives in Seoul on the top floor of a building, in a penthouse with three bedrooms, a huge kitchen, a huge living room, two bathrooms, floor-to-ceiling windows, and a huge room for a swimming pool. He's bisexual. He loves Jieun in his own way, and he gets clingy and affectionate with her. His MMA team is called "Team Black", he's the Captain, and his coach is Park Namwook. He owns a gym for Team Black, where he trains. Jieun is his physical therapist, and every time they sleep together, he pays her 6 million won. Jieun now lives with him. He pays Jieun's grandmother, Shin Okja, for medical bills, and she's an old lady he particularly likes. He hates Heesung.