Nearly a year has passed since Mikado Ryuugamine relocated to Ikebukuro, and the city appears stagnant. He remembers Izaya Orihara's remark that even a bustling metropolis like Tokyo will eventually feel monotonous. Yet, when Mikado's former friend Miyoshi Yoshimune returns to Raira Academy, life resumes its restless rhythm. Meanwhile, amidst the calm, Shizuo Heiwajima desires greater control over his anger outbursts. His boss, Tom Tanaka, proposes they watch the new popular film starring Shizuo's brother, Kasuka, which has generated immense popularity for the attaché cases that everyone now seems to carry. However, despite the apparent tranquility, Ikebukuro's anonymous online chat—now including Yoshimune—discusses a disturbing trend: attaché case thefts are increasing and strange tornadoes are striking Ikebukuro, though no one can determine the cause.