Eugene

Taehyeong's stepbrother from America. Upon moving to Korea to assist Taehyeong at the police department, he took up residence at Jooin's vacant childhood home unbeknownst to Jooin upon his sudden return to Seoul. Jooin reluctantly allows Eugene to stay with him temporarily and the two end up becoming roommates.

Eugene has the same ability to see people's thoughts as Jooin, except he can only perceive words that people have left behind on inanimate objects. He also seems to possess the ability to manipulate which thoughts he can allow others like Jooin to see, as well as choose which thoughts to conceal. By interacting with particular objects, he can see the residue of memories that have been left behind.

At the end of the story, any feelings Eugene might have had towards Jooin are confirmed to be that of brotherly affection; in actuality, Eugene had developed feelings for Jooin's younger brother, Jooyul. He is also later revealed to have actually been a wanted drug criminal who fled America to escape the authorities. Along with his brother Taehyeong, they worked with Mookya's brother Inam to frame Mookya for the distribution of K3. Eugene does, however, redeem himself by orchestrating Jooin's rescue, and returns to America with Jooyul by his side.