Affluent architects Ryota and his wife Midori face a terrible dilemma when they learn that their six-year-old son, Keita, was accidentally switched at birth and is not their biological child. In the wake of this revelation, Ryota's sense of fatherhood is shaken to the core as he witnesses both his wife's enduring devotion to Keita and his own conflicting feelings of nature versus nurture. Now his decision on which boy is truly his son will change the family's lives forever.