Biscuit

Son Jeseon has suffered from hypersensitivity to sounds since childhood. Worrying about his condition, his parents sent him to rehabilitation at a "sanatorium".
He is the only one who notices people invisible to others. Son Jeseon named those who have ceased... to exist for society "biscuit": their voices are not heard, and their presence is not noticed.
They gradually break down like dry biscuit, slowly disappearing without leaving even a crumb behind.
The strangeness begins when, at the rehabilitation center, Son Jeseon catches a horrifying smile from a neighbor. The young man is convinced that he wants to harm the biscuit next to them. Therefore, at all costs, Jeseon wants to unravel this mystery and help the one who fears to ask for salvation. Is it possible to gather the biscuit from which only crumbs remain?