Nagisa Furukawa (古河渚, Furukawa Nagisa), later Nagisa Okazaki (岡崎渚, Okazaki Nagisa), is the main female protagonist and love interest of Tomoya Okazaki from the anime series Clannad. She becomes Tomoya's girlfriend in the Clannad finale and eventually, Nagisa and Tomoya marry each other in Clannad After Story after Nagisa graduates from high school.
In Clannad, Nagisa and Tomoya first met one another on their way to school. Tomoya was walking until he noticed Nagisa who was talking to herself to gain confidence. Tomoya then spoke and encouraged her and they both walked to school together. Eventually, Tomoya and Nagisa met each other again the same day where they both had lunch together while also getting to know each other. Nagisa revealed to Tomoya of how she has to repeat her third year of high school once again due to her poor health and expresses her desire to join the school's drama club. Tomoya once again encouraged her, but sadly they both discovered that the drama club had been disbanded. However, Nagisa decided to restart the club and Tomoya began to help her. Ever since, Tomoya and Nagisa became friends and begin their goal to revive the club while their friendship further grows. Later as time went on, Nagisa and Tomoya began to develop more of a closer relationship to the point where Nagisa had invited Tomoya to move in with her family due to his strained relationship with his father.
Eventually, Tomoya and Nagisa had started to develop romantic feelings for each other and ultimately fall in love as Nagisa brings joy and hope for Tomoya and in return Tomoya always encourages and supports Nagisa. They also care a great deal for each other as Tomoya always worries whenever her health becomes more serious and Nagisa worries about Tomoya and his relationship with his father and occasionally encourages him to reconcile. However, despite their feelings they were both still too nervous to confess how they feel, but eventually the day after their school festival and upon spending the day together, Tomoya had finally confessed his love for Nagisa and she reciprocated and officially became a romantic couple.
However, while still in the beginning stages of their relationship, Tomoya and Nagisa still hadn't made real progress despite dating each other for several weeks, but eventually after some slight interference from Mei, Tomoya and Nagisa finally make some progress.
In Clannad After Story, Nagisa and Tomoya are in a serious and committed relationship after Tomoya confesses his love for her in the finale of Clannad. However, when graduation arrives, Tomoya and the rest of their friends graduate, but sadly Nagisa is force to repeat her third year of high school once again due to her illness, while Tomoya begins his life as an adult. Soon after, Tomoya begins living on his own and gets a job as an electrician, while they still continue with their relationship. Eventually, once Nagisa graduates from high school and gaining the approval of both her parents, Nagisa and Tomoya get married and begin living together.
Nagisa eventually becomes pregnant, but died from giving birth to their daughter, Ushio. Devasted, Tomoya goes into a five year depression and has Akio and Sanae look after Ushio. While during this time, he also greatly misses Nagisa, crying whenever he remembers or thinks about her. Eventually, after Tomoya realizes he is putting Ushio through the same relationship he had with his father, Tomoya and Ushio reconcile and she begins living with him. Sadly, Ushio later passes away when she succumbs to the same illness that Nagisa had. However, when Tomoya wishes for a miracle to go back in time, he originally tries to avoid his meeting with Nagisa as he believes he can change their fate, but realizing that he can't live without her, he calls out to her. Due to this and showing he doesn't regret their meeting, Tomoya is brought back to the day when Nagisa was in labour with Ushio, but this time she miraculously survives and from then on, Tomoya and Nagisa live a happy life together raising their daughter.