Because her mother was arrested for hurting her lover, the little girl Maki (Suzuki Rio) was sent to a child care institution called Little Wild Duck House. Here live children nicknamed Mailbox (Aina Ashida), Steel Beauty (Hyori Sakurada), Poverty (Konomi Watanabe) and Marbles who have left their parents for various reasons. Under the rule of the "Devil King" Sasaki Tomonori (Hiroshi Mikami), they are forced to show their cute and well-behaved side like kittens and puppies in the window of a pet shop, waiting for the appearance of new parents who can give them warmth and security. Maki got the nickname "Blunt Instrument". When she learned that she could not return to her mother, she identified with these new partners and tried to pursue their little happiness in the cruel adversity. Children who have tasted the cruelty of reality too early look at this weird world with cold eyes that do not match their age...