Hanabi Hyūga

is a member of the Hyūga Clan, the youngest daughter of the head of the clan, Hiashi Hyūga, and his likely heir. She is the younger sister of Hinata Hyūga, and cousin of Neji Hyūga.

Background
Since Hanabi is considered more powerful and confident than Hinata, Hiashi decided to focus his grueling training regime on Hanabi, to make her the next heir.

Abilities
It is noted during the Chunin Exams that Hanabi possesses a stronger Byakugan than her sister's but weaker than Neji's.

Chūnin Exam arc
Hanabi watched Neji's match against Naruto during the final round of the Chūnin Exams with her father, and was amazed to see that he had learned powerful secret techniques on his own. It was also indicated that she knew nothing about the failed attempt to kidnap Hinata that had resulted in Hizashi's death, mostly because she wasn't born at that time, as she did not know how her father could still be alive after the Land of Lightning demanded his death.

Anime Fillers
Hanabi appeared three more times in the anime; A flashback when Kurenai Yuhi came to talk about having Hinata join Team 8, at the funeral of the Third Hokage, and at Tsunade's inauguration, standing with her cousin Neji and his teammate Tenten.

Invasion of Pain arc
Although she didn't make an actual appearance, Hanabi was noted to be away with her father during Pain's attack on Konoha.

Trivia

 * Hanabi means "fireworks".
 * Hanabi also appears as a playable character in Naruto: Ultimate Ninja 3, Naruto Shippūden: Ultimate Ninja 4 and Naruto Shippūden: Ultimate Ninja 5.
 * As the younger sibling, there is a possibility she will be placed in the Branch Family and receive a Cursed Seal, once the next heir turns three. However, because her father felt that Hanabi was a more suitable heiress than Hinata, and because there have been several changes in the way the Hyūga family works, it is possible she might be exempt from this.
 * Since she is a girl, it is also possible she was never meant to have a Cursed Seal in the first place, as Japanese tradition usually only allows men to start a branch family.