Season 1 of Dark Blue Kiss premiered on October 12, 2019.

While Kao and Pete's relationship has grown stronger, they are still hiding it from most. Kao is closeted from his mother, and the fear of her finding him out looms over him and his relationship. In the meantime, Kao's mother introduces Non, her boss' son, as a student in need of Kao's tutoring. When Non shows interest in Kao, it fuels Pete's jealousy. The secrecy and jealousy put a strain on their otherwise thriving relationship.

Sun has begun to give up his unrequited love with Kao. And suddenly Mork is around a lot more. Whilst Sun pushes Rain to stay away from Mork, the younger man's uncontrollable behavior draws him in. Sun's seriousness settles Mork down. Despite their constant clashing, the two start to care for each other.