Hanabi Hyūga

is a member of the Hyuga Clan. She is the youngest daughter of Hiashi Hyuga, younger sister of Hinata Hyuga, and cousin of Neji Hyuga.

Background
Hanabi is Hinata Hyuga's younger sister. Her father considers her more talented than Hinata, but not as talented as Neji Hyuga, as he noted in the flashback in which Kurenai spoke with him about Hinata.

Chunin Exams
Hanabi watched Neji's match 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.

Post-Chunin Exams
Hanabi appears two more times in the anime; at the funeral of the Third Hokage, and at Tsunade's inauguration, standing with her cousin Neji and his teammate Tenten. In both cases, she appeared in crowd shots, and has not been seen in the manga since the Chunin Exams.

Other Appearances
Hanabi is mentioned in a recap segment on House Hyuga, in which Neji briefly struggles to recall her name. In it, Neji refers to her as "Hanabi-san", in contrast to referring to Hiashi and Hinata as "-sama", possibly because she is neither the head of nor the heir to the household.

Hanabi appears in Naruto Shippūden: Narutimate Accel, Naruto Shippūden: Narutimate Accel 2 for the PS2 as a playable character from the beginning (no unlock needed) and in Naruto: Ultimate Ninja 3 (this one you need to unlock).