Sena, a teenager with Arithmomania, is obsessed with the number 50, unable to escape its suffocating grip on her life. Each day is a battle of counting and arranging, trying to maintain a sense of control in a world that feels increasingly chaotic. But her family and friends dismiss her struggle as nothing more than a quirky fixation. Alone and misunderstood, Sena spirals deeper into her obsession, questioning if anyone will ever see the truth of her pain. As she confronts the terrifying possibility of never finding peace, the question remains: can she break free from the number that controls her?