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Behind the scenes of choosing an uncool guy

"I... am I really going to marry him...!?"
When Mitsuno visits the Shirazakura family for the first time in a while on an errand for her father, she is greeted by the three Shirazakura brothers, Toru, Masamune, and Kiyotaka.
Mitsuno is thrilled to be greeted by handsome men of different types, and for some reason she is led to a room that looks exactly like her own...?
Confused, she is told that she must become the wife of one of the three brothers in order for the Shirazakura family to buy the company and save it.
Confused, she begins to live with them, but is tossed about by Toru's debauched and sweet sex, Masamune's slightly rough and violent sex, and made to feel Kiyotaka's cosplay sex with a younger man... Mitsuno's mind and body become bound by all three men's sex appeal...?