Plot

Ryota is a successful workaholic businessman. When he learns that his biological son was switched with another boy after birth, he faces the difficult decision to choose his true son or the boy he and his wife have raised as their own.

Would you choose your natural son, or the son you believed was yours after spending 6 years together? Kore-eda Hirokazu, the globally acclaimed director of "Nobody Knows", "Still Walking" and "I Wish", returns to the big screen with another family - a family thrown into torment after a phone call from the hospital where the son was born... 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...—Wild Bunch

A young couple with a six year old son are advised that there was a mix-up at the hospital and their son Keita is not their biological child. the father, Ryota, is a hard working executive who spends very little time with his family and the job of raising their son is left to his stay-at-home wife Midori. Ryota is very competitive and struggles that his son is not and he creates hard feelings with his wife when he learns Keita is not his son and blurts out that that explains ii to his wife. MIdori had chosen to go to a country hospital near where she grew up so she would be close to her family when giving birth as she knew her workaholic husband would not be much use. MIdori is also held responsible for her choice of the hospital where the mix-up occurred. Ryota also implies that as the child's mother she should have recognized that the baby wasn't hers. The hospital and their lawyers arrange for genetic testing of the children to establish parentage. The mix-up was discovered when one of the other boys was tested prior to entering school and it was revealed he was not related to his parents. The two families are brought together and the other couple are small business people, Yudai and Yukara, with a repair shop they live at and two other younger children. MIdori had problems during birth and can have no more children. YUkara also has a job in a food shop. The two families are in very different economic situations and the father Yudai seems very interested in the potential financial settlement from the hospital. When the families meet the two boys are very dissimilar, Keita is smaller and more reserved and Ryosei is larger and outgoing. The lawyers and advisors all agree that the families should exchange the boys back to their real families. The two mothers are not certain and form a bond and alliance knowing that Ryota is the most forceful of the group. MIdori's mother is also troubled by the thought of exchanging the boys knowing how attached her daughter is to the boy. Ryota has a difficult relationship with his own father and his dad advises him that blood is important in families and horse breeding and is adamant that Ryota get his true son back. RYota's parents had separated and he had attempted to run away from his father who has custody and go back to his mother but his father brought him back. It turns out that he and his brother were raised lovingly by his step-mom. At the court proceedings the hospital nurse confesses to swapping the babies in some confused reaction to her raising her husbands children from a previous marriage. The other 3 parents are angry with the nurse but Ryota is more interested in getting his real son back. RYota, realizing that MIdori doesn't want to give up Keita, comes up with a scheme to offer the poorer family money and allow him and MIdori to raise both boys. Yudai and Yukara are offended and the plans proceed for the ultimate exchange. As a start, the families swap the boys on weekends over a series of months. Ryota describes this switching off of the boys as a mission that they have to undertake. It is obvious that the two families and their style of living and child rearing are quite different. After the exchange, Ryosei is not very happy without his siblings and his new father is much more remote and always working. Ryosei eventually runs away and goes back to his previous home and Ryota goes and retrieves him. Yukara facetiously suggests that maybe her and Yudai should keep both the boys. Ryota begins to reevaluate his behavior and his boss at work asks him to take a job that will free up his time for his family. Ryota and MIdori try to entertain Ryosei but he still expresses the desire to be with his other family. The three drive out to the repair shop and Ryosei announces that he is back home. Keita runs out the back and Ryota follows him. Ryota confesses he has not been a very good father and that he had failures and was too hard with his expectations. He announces the mission is over and hugs his son.