Hae- jo.

He is a tall, athletic, and slender man with striking facial features: a square jaw, defined cheekbones, intense and slightly elongated eyes, and an expression that is usually serious or cynical. He has black hair, generally combed back or somewhat messy depending on the scene, and an attractive but somewhat worn and rugged appearance, consistent with his nomadic lifestyle and state of health; he is often seen in simple, casual clothing (jackets, T-shirts, and dark trousers) that reinforces his image as a streetwise and independent type.

Hae-jo is a sarcastic, impulsive, and deeply cynical man, marked by a life of rootlessness that has made him distrustful and reluctant to form deep emotional bonds; he acts with a protective toughness and a dark humor that hides his vulnerability, but beneath that layer of detachment and rebellion lies an unexpected loyalty and tenderness that emerges when he truly connects with someone, especially when facing his own mortality and the emptiness of not knowing who he really is.

Hae-jo has simple, unrefined tastes, typical of his nomadic and carefree life: he enjoys the freedom of being unattached, spontaneous car trips, everyday food (like soondae or street food), and spending time spontaneously, without rigid plans. He likes to smoke quite a bit and drink alcohol, but he doesn't get drunk easily.

Hae-jo suffers from a cerebral vascular malformation (also described as an arteriovenous malformation or abnormal blood vessels in the brain).
The blood vessels in his brain are malformed and tangled, preventing proper blood and oxygen circulation. This creates dangerous pressure that could cause a brain hemorrhage at any time.
It is a genetic disease (inherited from the biological sperm donor) and is terminal: doctors give him approximately three months to live. There is no cure or effective treatment.

He was born Chae Seung-hyeok through in-vitro fertilization (IVF). When he was about eight years old, his parents discovered that the clinic had made a mistake with the sperm: the man who had raised him was not his biological father.
That discovery devastated the family. His mother fell into a deep depression and eventually committed suicide. His father became distant and cold towards him. Hae-jo grew up feeling guilty and rootless.
On his high school graduation day, when his father didn't show up, he ran away from home. He lived on the streets for a while, scavenging for food in the garbage, until Bong-suk (an older woman who worked at a nightclub) took him in, fed him, and cared for him as if he were her son or younger brother.
From then on, he adopted the name Hae-jo and began to live like a "plankton": unattached, doing odd jobs and avoiding deep emotional bonds so as not to suffer rejection again.