Nagisa is a young girl in Tomoya's class. She is actually one year older than Tomoya, since she is repeating her third year due to a nine-month illness. Nagisa wants to reestablish the disbanded drama club, and her attempt to do so is the main focus of the Clannad anime.
The bigger part of Clannad’s story focuses on Nagisa, her attempt at reestablishing the drama club, and her relationship with Tomoya. Nagisa met Tomoya on the first day of school on a long hill path near the school. After befriending her, Tomoya is told about her dream of joining the drama club. After discovering that the club has been disbanded, they decide to recreate it. Unfortunately the deadline for advertising for new members has passed. In order to create a club one needs at least three members, as well as a supporting teacher.
The only teacher left is Koumura, who asks them to talk to the chorus club which he currently is responsible for. After hearing the story of Rie, one of the chorus club members, Nagisa gives up on the drama club. Rie had once been a splendid violinist, getting numerous awards and offers for studies abroad. However, she got in an accident which hurt her hand, preventing her from playing the violin. Her friends decided to create a chorus club for her, as she is also very talented at singing. When Youhei hears about the story he is infuriated, and demands a basketball match against the school’s basketball team to show the chorus club that they can’t hide behind Rie’s handicap. This succeeds, and the clubs decide to share Koumura.
After a falling out with his father, Tomoya is offered by Nagisa to stay at her place until things settle. Tomoya accepts, and moves in at the Furukawa’s. Nagisa writes a monologue play for the drama club, which for some reason is very similar to Tomoya’s dreams about the illusionary world. Nagisa says the play is based on a story she vaguely remembers from her childhood, and Tomoya decides to find out more. While searching for old storybooks with Nagisa’s father, he gets to know a secret about Nagisa’s illness – her parents had given up their dreams in order to take care of her. Shortly Nagisa also finds out, and feels guilty about it. She thinks living out her actress dream would be wrong, since she prevented her parent’s from living out theirs, and decides not to perform the play. Her parents tell her that since her illness, their dreams had been for their daughter to live out hers, and she decides to perform the play after all.
In After Story, Nagisa gets ill once again, forcing her to repeat her third year again. Eventually Nagisa graduates and soon after gets married to Tomoya, eventually she would give birth to a child named Ushio before passing away.
Her father is Akio Furukawa and her mother is Sanae Furukawa, and they both run the Furukawa Bread Shop.
Clannad is an anime movie based on the game by Key. This movie is not relevant to the anime but creates an alternative storyline.