In his early years he was a researcher together with Miena. He became a Doctor later on and after the demans attacked his hospital, he lost all hope and decided to commit suicide. He was stopped by Rano who reminded him he was still alive, and that he refused to die until he found his sister. Sam decided to help Rano in his quest to find Lucy, having been given a reason to go on living. Together with Rano, Miena, Lessa and Yuzuru the group set about eradicating and learning about the demans.
Young-sam has the ability to heal anyone. He managed to find a cure for Ryan, who was dying from an incurable illness and was about to administer the treatment, having performed a successful trial, only to find Ryan having lost hope, and choosing to become a deman, killing the staff and patients at his hospital. It was this incident that lead Young-sam to try and take his own life. It is prophesied that Saint Elsade's blood flows through him, and he will be the one to undo the deman curse.
Dr. Jin Young-sam wakes Rano up, by blasting a siren through his alarm. Having gotten Rano's attention, Young-sam gives Rano the location of a Deman disturbance.
Young-sam treats the girl Rano rescued from Demans the night before. He tells her about him and Rano going out hunting every night and killing Demans. He takes her home after giving her a flyer with Lucy's picture, asking her to inform them if they see her. He prepares dinner and asks Rano to come and eat. During dinner, Rano asks about Ares. Young-sam replies he's heard rumours about him being the leader of the Demans but is unsure. Later that night as Rano is on a stake-out, Young-sam tells him the Demans are close to his location and he'll give him a signal when they're close by. He warns Rano, but Rano is unable to react on time, resulting in him being kicked in the face by Lessa.
Having injured Lessa, Rano brings him home. After scolding Rano, Young-sam treats Lessa and asks him if he's in any pain. Lessa doesn't respond, so Young-sam says, he'll just take a look at his teeth. Checking Lessa's teeth, Young-sam realises he isn't human and guides him to the other side of the room, making him sit in a large stone chair. He restrains Lessa, and after Rano protests, he informs him Lessa isn't human. Rano thinks it's strange for a Deman to not have horns and intends to make certain by burning him with a high intensity lamp. Young-sam battles Rano for the lamp, stating Lessa is worth studying. The two argue while still grappling for possession of the lamp, while Lessa watches silently. The lamp switches itself on, and Lessa flinches at the brightness of the light but is otherwise unharmed. Young-sam gathers some equipment and tells Rano to guard his sample, while he conducts research in his lab. He leaves entrusting Lessa to Rano.
Having heard the commotion Young-sam runs downstairs. Young-sam asks Rano, what he did with his sample, as Rano tells him that's not important, right now, as he needs medical attention. Young-sam looks at Rano asking if it's blood on his face, having thought it was Rano's moustache.