"Sachi" is a high school student. In the beginning of the story, her real name is unknown, as she is only referred to as "XXX-San" on television and by two former classmates who recognize her on the street. "Onii-san", her kidnapper, gives her the name "Sachi", which comes from the word happiness in Japanese, in replace of the name she had during her old life. 

That day, she was abducted. But to her, that abduction was a ray of hope -- the beginning of a new life. The girl promises to marry her abductor, and the abductor offers plenty of "happiness." This is the story of an abductor and his victim... How could it be so warm?
 
(Source: Crunchyroll)
 
Note: Chapter count includes one bonus chapter.