Izumi Uchiha

was a kunoichi from Konohagakure and a member of the Uchiha Clan. She was a friend of Itachi Uchiha since their childhood, and was infatuated with him.

Background
Izumi happily lived outside the Uchiha Compound with her mother and her father. After the Third Shinobi World War, Izumi met Itachi, offering him to play with her and her friends. Itachi however politely declined, saying he needed to go train. When her friends felt insulted and began throwing rocks at him, Izumi begged them to stop, despite Itachi nonchalantly dodging every rock. Once Itachi caught one of the rocks and used it to deflect the kids' entire barrage, Izumi and the other kids were left speechless.

While initially having a carefree life during her early childhood, her happiness was cut short during the Nine-Tails' Attack on Konoha when her father sacrificed his life to save her and she blamed herself for not being strong enough to save him. Overcome with such emotion, she awoke her Sharingan and passed out until the attack was over. After the incident, her mother moved the two of them with the rest of the Uchiha clan.

Itachi Shinden: Book of Bright Light
In her early Academy days, she met Itachi in the classroom next to hers, where she became infatuated with him. Eventually, she earned his acceptance when she defended Itachi from older Academy students like Tenma Izumo (one of Itachi’s future team-mates), who were jealous of his advanced skills by using her Sharingan.

When she was eleven years old and about to graduate early, Izumi and Itachi stopped at a tea shop for a rest where Itachi's former teammate Shinko Inari was now a waitress at. Here Itachi questioned her on her desire to grow stronger. She explains her desire to grow stronger to help others is inspired by her father’s sacrifice, but Itachi’s insistence on her abandoning her resolve made her cry and she left.

Eventually, Izumi and Itachi were seen as a "couple" by many of their peers.

Itachi Shinden: Book of Dark Night
During the Uchiha Clan Downfall, Itachi came to her to begin the massacre with her as he was told by Danzō Shimura that he could only spare his little brother Sasuke Uchiha. Believing that ending her life first would quell his inner doubts, he proceeded to kill her and her mother first. As he lured her mother away, Itachi approached Izumi and placed her in an extremely powerful Tsukuyomi where she lived the entirety of her life in 0.000000001/th of a second. In her dream, she became a chūnin, retired from shinobi life to become Itachi’s wife and raise their children, and lived to become eighty years old before dying of old age alongside Itachi. Because her mind was departed from reality in such a manner, Izumi collapsed into Itachi’s arms dying. Izumi thanked Itachi for giving her the life she wanted with him, even if it was a dream, and Itachi thanked her for loving him as she passed away peacefully.

Personality
Izumi was described as a kind and considerate girl for an Uchiha. After her father’s sacrifice, Izumi was traumatised and blamed herself. Since then, she decided to live up to her father’s example by becoming stronger so she could help others like her father did. Because of this, Izumi never fell into the Curse of Hatred, unlike the vast majority of her fellow clansmen. Even though she appeared to distrust the rest of her clan like Itachi and Shisui Uchiha, she still had great pride and faith in her clan as she refused to believe an Uchiha would’ve summoned Kurama to cause such death and destruction that took her father’s life.

Her desire to help others weighed heavily on her, as she was deeply distressed she wasn’t progressing as quickly as Itachi, who she used to measure her abilities against. When Itachi tried to convince her to abandon her goal of helping others because of her innocence and weaknesses, she was visibly hurt.

Abilities
When her father died during Kurama’s attack on Konoha, she awakened her Sharingan, even earlier than Itachi himself. However, she was not able to control it, fainting every time she activated it as she lacked the necessary chakra levels. This did not get better as she still fainted even when she was getting closer to her graduation into genin.

It was implied that Izumi was skilled as a kunoichi for graduating a year earlier than others.

Trivia

 * means "fountain".