Gap-Su Seo is a member of Joon Shin's criminal gang. Out of all the members of Joon Shin's gang, Gap-Su is the most immoral and impulsive to the point of disobeying Joon's orders. He is willing to do many immoral things to others to satisfy his needs. He is also petty and vengeful. His impulsiveness and unreliability keeps him relatively low in the gang's pecking order, as he was the only gang member not given any important task to fulfill.