During his childhood, Gabriel had suffered a trauma from a demon invasion on his village. 7 years later due to his past tragedy, he is now a world renown demon hunter known as "The Demon Executioner". But there is something in Gabe's past that he doesn't know about and that's the fact that deep inside of him, there is something inside that he despises more than anything and he's one of them. How will Gabe continue his life knowing that he's a half demon?

Nam Shin-woo is the third son of Oh Ro-ra and Nam Jung-woo. He had a girlfriend named Go Hae-ri whom he loved so dearly. Shin-woo and Hae-ri are together and had the most perfect relationship until Hae-ri dies because of a deadly disease that led her into a very sick stage. To take away his pain, Shin-woo attempts to bring Hae-ri back to life by creating an AI robot modelled after his desceased girlfriend, naming her SUJI 3 and inserts their memories into her system. They are so happy to be finally together again until his best friend, Kang Ji-seok, betrayed him. Will Shin-woo be able to find the key to Hae-ri's death and discover the secret that lies behind Ji-seok's real identity? And will he be able to uncover the secret that Ji-seok has been hiding from him?