As punishment for embezzling funds from her husband's company, Rui Nego to is entered into "Chiku Kō GP," an anal review panel attended by anal enthusiasts. Locked in a dark prison cell, the evaluation begins with numerous analysts inspecting her anus, sniffing it closely and using magnifying glasses to count every wrinkle. To compete for the title of number one anus, she undergoes nightly anal training sessions. Enduring humiliation for her husband's sake, Rui gradually awakens to new physical sensations through her anus, ultimately realizing her true potential as an anal slave.