Yūgao Uzuki

is a member of the Konoha's ANBU, and was Hayate Gekkō's lover.

Invasion of Konoha Arc
During the invasion of Konoha, Yūgao visits the memorial stone where Hayate's name is engraved. She swears to avenge him before leaving with her ANBU squad. She visits the memorial again during the Third Hokage's funeral, where she has a conversation with Kakashi.

Twelve Guardian Ninja Arc
Yūgao briefly appeared during the Naruto: Shippūden anime, catching Sora spying on Danzō's interrogation of Tatsuji. They apprehended him and turned him over to Tsunade.

Invasion of Pain Arc
In the anime, Yugao is one of four ANBU tasked with protecting Tsunade as she is using Katsuyu to heal the villagers.

Other media
Yūgao 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, canonically, 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. However, she does not appear in the story after this. She also has a Team Special Jutsu with Kakashi, most likely due to the fact that she refers to him as her superior.

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

Trivia

 * "Uzuki" is the old name for the fourth month of the Japanese lunar calendar, while "Yūgao" means "moonflower".
 * She also appears one time talking to Kakashi and in Naruto: Clash of Ninja Revolution 2 and Naruto Shippūden: Clash of Ninja Revolution 3 she has a tag move with Kakashi as well.