Original Webtoon

Kwon Ga-eul, the younger brother, always invites someone with similar features to his older stepbrother to his room.
Seo Yi-sol, the older brother who lives with him, is the only one who has not been able to enter his room.
After 6 years of not being able to cross the line that Ga-eul drew, Yi-sol wants to cross that line.

Note: The third story from series Family Disqualification.