Kang Joon was a tall, handsome man with pale skin and either white or silver hair. He is always shown in formal clothing and is deceased at the time of the current storyline.
Kang Joon was often referenced whenever anyone explained the origins of Meduza, as he is a central figure in her emergence.
He was introduced in a flashback from forty-five years before the current storyline. Seo Gang Min and Kang Joon arrived in Seoul in 1960 and on their way, Kang Joon spotted a beautiful girl in pigtails. He yelled for the driver to stop. The girl's name was Ji So Hee.
For Kang Joon, Ji So Hee was a charming flower in a dismal country called Korea. He begrudged going there until he fell in love at first sight. And despite So Hee's constant rejection, he remained persistent in his advances, even thinking her resistance enjoyable. Over time, however, he became increasingly frustrated with her defiance.
With my looks and status, there isn't a woman who doesn't accept me? Why does she hate me?
Adamant that there was no other woman for him, Kang Joon refused to consider other women. Over time, he lashed out violently at So Hee. The first time he became angry, Kang Joon bit her. Devastated at his own actions, a heartbroken Kang Joon carried her body in the rain until he ran into Gang Min, who demanded to know what happened. Thinking So Hee was dead, the pair fought, only stopping when they realized that So Hee had been resurrected as a vampire.
So Hee as a vampire was even more beautiful and Kang Joon's obsession grew. Until finally, he resolved to stop asking for her hand. If she refused to marry him this last time, he told Gang Min he would not ask again. But when Kang Joon walked through the gates of So Hee's home, he found out she had a fiance and flew into a rage.
Realizing the reason why he was rejected was because of a normal human man, Kang Joon killed her fiance in anger. So Hee vowed to get revenge afterward as she fled carrying her lover. Both brothers felt guilty afterward and for a long time, Kang Joon would not leave the house. When he finally did, a search party was assembled and he refused to accept any suggestions that So Hee may have died during her absence.
Sometime later, So Hee finally returned. Just as Kang Joon had hoped, she seemed to have thought it through and finally accepted him. So Hee was said to have had a sly smile on their wedding day. Later, on their honeymoon, Seo Kang Joon was discovered on the bed, completely drained of blood.