On the way to school one day, Tomoya Okazaki meets a strange girl talking to herself named Nagisa Furukawa. Later in the day, Tomoya has a conversation with Nagisa during lunch and learns that she is repeating her last year of high school, and wants to join the now-disbanded drama club. After school, Tomoya goes to Nagisa's family bakery and meets her parents; he is invited to have dinner with them.

Nagisa admits to wanting to restart the drama club, and Tomoya helps Nagisa to create advertisement posters which they place around school. At school that day, Tomoya meets two other girls: a strange genius named Kotomi Ichinose, and a first-year named Fuko Ibuki. Later that day, Nagisa finds out Tomoya used to play basketball, and invites him to play a game the next day. However, it is later revealed that his father injured Tomoya's arm in a fight; as a result, he is unable to play basketball anymore.

Tomoya runs into Fuko again at school, and she tries to invite him to her older sister's upcoming marriage ceremony, but Tomoya is not interested. Tomoya gets Youhei to help reform the drama club by bribing him with bread from Nagisa's family bakery. Nagisa tries to get the help of Ryou and Kyou in reforming the drama club, and Tomoya even tries to ask Tomoyo and Kotomi if they would like to join; Tomoyo is trying to become student council president, and Kotomi does not give an answer. Tomoya and Nagisa later go see Fuko about the club, and he discovers from Nagisa that Fuko is supposedly unconscious in a hospital.

Tomoya, Nagisa, and Fuko spend the night at school having a pre-celebration for Youko's wedding. In the morning, Tomoya and Nagisa have forgotten about Fuko and cannot see her. Both Tomoya and Nagisa later feel that there is something important that they are forgetting, and finally remember about Youko's wedding, which is also when they are able to see Fuko again. On the wedding day, initially the only students to arrive were Tomoya, Nagisa, and Fuko, but after the ceremony it is shown that everyone who had received a starfish came to the wedding. Fuko ultimately disappears after thanking Tomoya and Nagisa for what they have done, and congratulating her older sister. A rumor still persists at Tomoya's school of Fuko as a cute girl who is constantly running through the school.

Kotomi finally leaves the house to find that Tomoya worked in the garden all night long and had fallen asleep. When she returns to school, Tomoya, Kyou, Ryou and Nagisa are all waiting for her. The mysterious stranger whom she was so frightened of, believing he wanted to steal her parents' thesis, is there as well. Kotomi and her friends find out that he is her legal guardian, and that there never were any written notes for the thesis after all. The envelope Kotomi set fire to, and felt so guilty about, was nothing important. The stranger also has a birthday gift for her: her parents' suitcase, which survived the plane crash and was passed from hand to hand for years until he found it. Inside is a teddy bear, Kotomi's gift request to them before they left, and an affectionate letter. Kotomi, holding the bear, is so happy that sparkles literally fill the room, and makes peace with her parents' deaths at last.

The drama club is finally re-established and Koumura is shared with the choir club. Tomoya's home room teacher goes to Tomoya's house to ask his father about his future, but Tomoya's father says that is something that Tomoya has to decide for himself. Seeing the strained relationship between Tomoya and his father, Nagisa offers to have Tomoya stay over at her house for the time being, which he accepts. After coming home from school, Tomoya finds several small kids in Nagisa's house, and finds out Sanae is instructing them in a cram school. Nagisa confides to Tomoya that she feels she did something really bad to her parents in the past, but she cannot remember what it is, and her parents say that she must be imagining it.

After hearing Nagisa talk about the story for the play she wants to perform, Tomoya tries asking Nagisa's parents about it, but they do not know any story like that. After Akio catches Tomoya and Nagisa in the shed, he tells them to leave, and later brings Tomoya aside to tell him about what happened in the past. Ten years prior, Nagisa was running a high fever one snowy day, and in the midst of this, her parents had to work, so they left her alone for a couple of hours. When Akio returned, he found Nagisa collapsed outside as she had been waiting for them to return. Due to Nagisa nearly dying, both of her parents abandoned their jobs and their dreams in order to protect Nagisa. Akio tells Tomoya not to tell either Sanae or Nagisa about the story since he does not want it coming up again. Tomoya goes on a picnic with Nagisa's family, and during a baseball game with some local young boys, Nagisa accidentally confesses her love to Tomoya indirectly.

In an alternative timeline where Tomoya and Tomoyo are dating, Tomoyo becomes student council president, but bad rumors start around the school due to Tomoya's bad reputation. Tomoyo becomes busy during the school festival, and continues to be so while she attempts to save the sakura trees in town. Tomoya realizes that he is holding Tomoyo back from greater things, and despite both sides being reluctant, they break up. Time passes as Tomoyo's reputation builds and Tomoya and Youhei watch on the side through her many accomplishments, one of them being ultimately saving the sakura trees by the winter. At that time, Tomoya and Tomoyo meet and talk for the first time in months and they decide to become a couple again.

Mei has become worried about her older brother since he still does not have a plan after high school, and comes to stay at Nagisa's for the time being. Based on a fleeting comment by Youhei, Tomoya gets the idea to ask a girl to pose as his girlfriend so Mei will stop worrying about him. Youhei goes around with Tomoya and Nagisa asking Ryou, Tomoyo, Kotomi, and Yukine, but no one can help him. Sanae overhears Youhei's trouble and decides to be his fake girlfriend if it will help push him in the right direction in life. Youhei, however, still believes her to be Nagisa's older sister. When Mei meets her brother's "girlfriend", Sanae is posing as a student from Tomoya's high school.

Tomoya, Nagisa, and Youhei finally find out that Yukine is respected by the two rival gangs in the city since she helps both sides' members after they get hurt. Her older brother is the leader of one of the gangs, and a young boy named Yu comes to her to find his older sister who apparently is dating a guy in Yukine's brother's gang. Youhei tells Yu that he is Yukine's brother for a time, but the truth is later revealed after Yukine takes Yu, along with Tomoya, Nagisa, and Youhei, to a bar where her brother's gang hangs out. Yukine's brother has been in the hospital since he saved a friend and got in a car accident. While heading home, three members of the rival gang think Youhei is Yukine's brother and try to fight him and Tomoya, but Tomoyo intervenes, stopping them single-handedly.

Tomoyo speaks to Yukine and the others about hearing that the police will start to get involved in the fight between the two gangs if it gets any worse. Trying to stave off a major brawl, Yukine goes with Tomoya to try to talk the other gang out of a fight, and the leader settles on a fight between him and Yukine's brother Kazuto. Youhei reluctantly goes to stand in for Kazuto, but is incapacitated along with everyone else but Tomoya after eating Sanae's bread, so Tomoya fights the leader of the opposing gang. Yukine impersonates Kazuto to end the fighting, and finally reveals to everyone that did not already know that Kazuto has been dead for some time, and his wish was to end the fighting in the town. At the cemetery, Yukine pays respect to her dead brother and the rival gang joins in. With the rivalry resolved and peace restored, Tomoya witnesses a glow rising into the sky.

Yusuke tells Tomoya a little about his past and how he met Kouko in high school. After graduating, Yusuke went on to become a successful singer-songwriter, but ultimately it all came crashing down and he started taking drugs. When he came back to the city and saw Kouko again for the first time in years, he regretted not continuing to sing for her sake. Tomoya is offered a new position as a manager in a new electrician firm, but the deal falls through when his father is arrested. Tomoya is enraged that his father is still managing to mess up his life. Tomoya finally proposes to Nagisa, and she accepts.

While on the trip, Tomoya buys a toy robot he picks out for Ushio to play with after they arrive in the countryside. The next day, after staying at an inn the previous night, Tomoya and Ushio take a walk through the area and come across a field of flowers. Ushio plays in the field as Tomoya watches, but Ushio soon loses the robot in the field; they try to look for it, but to no avail. Remembering something from his past, Tomoya goes off to another area and meets his grandmother Shino Okazaki, his father's mother. She tells Tomoya how he came here with his father shortly after his mother died, and Shino tells Tomoya how his father worked very hard to support him over the years. Tomoya finally comes to terms with his father, and realizes he is not a bad father. When they go back to the field where Ushio is, she still cannot find the robot, and does not want to stop looking because it was the first thing her father ever gave her. Tomoya realizes his previous mistakes and vows to try his best for Ushio from now on, who is very happy at the prospect of being with her father. On the way home, Tomoya starts telling Ushio about Nagisa for the first time.

The girl in the Illusionary World is dying in the snow, and the robot regrets having her take the journey. The girl can finally hear the robot, and tells him that they once existed in another world. As she hums the tune of "Dango Daikazoku", the Illusionary World starts to collapse. As the robot is swept away, the girl calls him "Papa" and disappears with the world. Back at the hill, Tomoya calls after Nagisa, and she is glad that he did so. Nagisa brings Tomoya through time, and together the voices of the robot and Tomoya note the end of his long journey. Tomoya awakens to Ushio's birth, but this time, Nagisa miraculously survives. After Nagisa watches Tomoya give Ushio her first bath, she and Tomoya see that countless orbs of light are floating throughout the city outside the window. They both sing to Ushio and from then on, Tomoya and Nagisa experience a happy life raising their daughter together, finally free of their cursed fate.