A mysterious girl wearing only underwear and a collar suddenly shows up at the protagonist's door. Though he intends to send her away, he ends up taking her in and naming her Kuro, treating her like a pet dog. What starts as a playful game of obedience and control gradually becomes more intense. The protagonist becomes increasingly possessive and begins enforcing more extreme forms of "training" to assert his dominance. As Kuro is pushed further into these roles, she eventually faces a situation in public that tests her boundaries, involving humiliation and loss of control.