Shimai: Love Doll (2000)

Makoto is a successful businesswoman who must balance her time between work and caring for her mildly retarded sister, Chinatsu. Makoto believes she's met the man of her dreams and wants to get married, but will he agree to let Chinatsu live with them? will Makoto be forced to choose between her love and her sister? And what about the young man who's been showing an interest in Chinatsu?