Yūgao Uzuki

is a member of the Konoha's ANBU, and was Hayate Gekko's lover. After Hayate was killed by Baki, Yugao swore to avenge him. As it is unlikely she knows who killed Hayate, it is possible she meant she would get her revenge through fighting against the invasion.

Yugao briefly appeared during the Naruto: Shippūden anime, catching Sora spying on Danzo's interrogation of Tatsuji. They apprehended him and turned him over to Tsunade.

Other media
Yugao is a playable character in Naruto: Clash of Ninja Revolution 2. In the game, she possesses techniques similar to Hayate's. While it is unclear if she uncovered the identity of Hayate's killer, her battle cry when using Dance of the Crescent Moon when fighting Baki in the game changes to, "Revenge ... for Hayate!" She has a small role in the game's storyline, appearing in the antagonists' hideout to save Naruto, Kakashi, Gaara and Sakura from a group of missing-nin, stating that the ANBU would take care of the situation. She also has a team special with Kakashi, most likely due to the fact that she refers to him as her superior.

Yugao also appears as a playable character in Naruto Shippūden: Gekitō Ninja Taisen! EX 3. She is also the model of the female ANBU party member in Naruto: Path of the Ninja 2, but the player can bequeath her with any name they please.

Trivia

 * "Uzuki" is the old name for the fourth month of the Japanese lunar calendar, while "Yugao" means "moonflower".