Chizuru Nagahama, a college student, is troubled by a promise she made with her step-brother, Kirito, when they were kids. "Until you meet someone special, I'm going to always be yours." The promise escalated over the years, until Kirito, who grew to be very handsome, started taking care of her physical desires...!! An enchanting brother making his sister give in to her desires. A story of forbidden love.