In the middle of class at a certain school, Yokoi Rumi, a diligent student, has her in-class life turned upside down when her desk mate Seki Toshinari begins to play by himself at his desk in class. Although Rumi is irked by Toshinari's distracting yet intricate playtime, she finds herself being drawn into his interesting hobby. Never being able to focus, Rumi observes Seki's stunning ways of slacking off in class.

Source: ANN

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Side story: Tonari no Seki-kun OAD