Ryota has earned everything he has by his hard work, and believes nothing can stop him from pursuing his perfect life as a winner. Then one day, he and his wife, Midori, get an unexpected phone call from the hospital. Their 6-year-old son, Keita, is not 'their' son - the hospital gave them the wrong baby.

Ryota is forced to make a life-changing decision, to choose between 'nature' and 'nurture.' Seeing Midori's devotion to Keita even after learning his origin, and communicating with the rough yet caring family that has raised his natural son for the last six years, Ryota also starts to question himself: has he really been a 'father' all these years...