Seo Gang-Min is the current head of the vampire clan and the father of Seo Kang-hoo and Seo Ji-hoo. He is also the strongest vampire and a central figure in the incident that lead to the appearance of Meduza. His powers are unknown but it is shown that he can easily regain and show both his own and the memories of others.
Gang-Min is shown to be a very kind and good looking vampire with the appearance of a young man. He has straight, shoulder length, dark hair that is slightly wavy at the ends but combed back and parted to the side on the upper-left. As a youth, his hair is identical to his son, Seo Kang-hoo, though slightly shorter and with less waves.
He first appears in the story as a mysterious figure that meets Yoo Da-in and tells her the truth about herself and her mother, Meduza, explaining the method to break free from her. Then, he later reappears when Yoo Da-in drinks poison. The antidote was his blood and he readily agreed to save her life, saying that his sons had completely fallen for her. But he notes that it will be troublesome if Yoo Da is as indecisive as her mother.
Forty-five years from the current storyline, Seo Gang Min, with his brother, Kang Joon, arrived in Seoul and on the way to their destination, Kang Joon spots a beautiful girl in pigtails. He demands the driver to stop the car as a curious Gang Min looked on. Both fall in love with Ji So Hee at first sight but Gang Min holds back because of his brother's feelings.
Over time, however, he became increasingly concerned with his brother's mental state and is horrified when Joon bites her in an angry frenzy. Miraculously, she survives but other than the hate she felt for the vampire that killed her family, her feelings remained unchanged. Even so, he was secretly pleased with her persistent rejection of Kang Joon. He feels no different when Joon finally declares that he will give up if she rejects him this last time. But when the pair discover that she has a fiance, they are overcome by hate and jealousy and Gang Min watches as Kang Joon murders her human lover, while a crying So Hee screams for hep in the background.
Afterward, Ji So Hee swears revenge and flees with her lover's body. Times passes without a trace of So Hee and the brothers are left to regret their actions. They both conduct their own independent searches and after looking for a long time, Gang-Min meets her again. She is suicidal and he is only able to convince her to keep living by offering her a chance at revenge. He teaches her combat and allows her to drink his blood until he realizes she is the "Meduza" that has been killing pureblood vampires. They have a confrontation and when it is revealed that Gang Min never meant to allow So Hee to take revenge, So Hee is outraged and scorns his confession of love.
So this is your real intention! You are no different from Kang Joon!
He doesn't meet her again until his brother's wedding. When his brother is discovered dead on his honeymoon, Gang Min is not surprised and succeeds his brother's position as heir of the family. Because of his position, he is pressured into an unwanted engagement. During this time, he meets So Hee again. The pair reconcile and after spending the night together, So Hee leaves a note for Gang Min to meet her again. This time, they plan to run away together. But So Hee never shows and Gang Min is escorted back by guards and forced to go through with the wedding.
Forty-five years later, he is stabbed by a thrown knife meant for So Hee, now known exclusively as Meduza. The clan head falls to the ground, coughing. Gang Min declares his love for her again and forces his blood on her in order to help her understand his actions. She receives his memories of the past and cries with the realization, holding her former lover in her arms. She explains that she found out about his fiance before meeting him and that her pregnancy was not why she abandoned him. He dies as she professes her love for him and gives his corpse a tear stained kiss.