"If I were to cheat on you, I would know it by your breath."

Shiho and her boyfriend Toru have been living together for 10 years since they met in high school.

After meeting up after work, they stop by the supermarket, share household chores, finish dinner, and sleep in the same bed.
As they are about to end such a peaceful day, Shiho suddenly notices that the 8th is circled on the calendar.

October 8 is the anniversary of their relationship:
"I see! Toru would surely choose this day to propose!"　

Shiho then learned for the first time that her boyfriend was not....