Yuutousei na no ni Kouen no Are ga Hairu made Hirogechaimashita ~ Koukakurou Nikai

Madoka Arisugawa is an honor student whose social disposition is sort of her weak point. One night she comes across a spectacle in the shopping district. It's the figure of a girl, naked, and able to take not just an arm but a wide car stop pole into her asshole.
That scene, so far removed from her own sense of reason, makes her heart tremble even long after she returns home, sending ripples through her settled lifestyle.
How many times now has the image of that chalky pale body taking in that silver pole come to her mind?

[edited from DLsite English]