Yūgao Uzuki

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

Yugao briefly appears during the Naruto: Shippūden anime, catching Sora spying on Danzo interrogation of Tatsuji. They apprehend him and turn him over to Tsunade.

Other media
Yugao is as 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 story 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 bequeaths 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".