Baek Ji-Hwan is used to being alone. Gay, kinky, and unapologetically himself, he never fit anywhere easily. When Seo Jae-Rim enters his life, Ji-Hwan thinks he’s finally found the perfect partner. Until the truth comes out: Jae-Rim is straight, has a girlfriend, and wants Ji-Hwan’s help learning BDSM for her sake. Ji-Hwan rejects him immediately, but Jae-Rim keeps coming back.
Unseen by everyone else, Jae-Rim becomes the one presence Ji-Hwan can’t ignore… his invisible partner.(Source: Lezhin US)
— Description from AniList community (anilist.co).