Hotaru (ホタル) is the granddaughter of the former leader of the Tsuchigumo clan, En no Gyōja.

One day Hotaru was under attack by a group of ninja who were actually after Utakata. Utakata saved Hotaru from the ninja, but was wounded in the battle. Hotaru ran for help from her fort, saving Utakata's life, causing him to become indebted to her. After this, he became a sort of master to Hotaru in order to hide from anyone who is after him. Later she finds him sleeping under a tree and Utakata got angry when Hotaru called him master, saying that the relationship between a master and a student is not something you can count on. Utakata reluctantly begins to teach her the Water Walking Exercise first, believing that she wouldn't master it. In the morning, she shows that she was able to stand on top of the water by training all night. Next, Utakata taught her Water Release: Violent Water Wave, once again believing that she would not be able to master it without water-natured chakra only to discover she does possess water-natured chakra. She later found Utakata under a tree and showed him the she again mastered the technique much to his suprise.

When a group ninja came looking for the Tsuchigumo clan's kinjutsu, Tonbee had Hotaru, along with Utakata, take the clan's forbidden jutsu so that ninja could not retrieve it. While traveling, Utakata got upset at Hotaru for calling him master (師匠, shishō), at which point Naruto arrived, believing Utakata to be attacking Hotaru. Hotaru broke up the fight and Utakata left her, deciding that Team 7 would be capable in protect her. As she watched him float away in a bubble, she tried to convince him not to leave, but was unsuccessful in doing so.

While on the way to the clan's secret village, Naruto argues with her only for Yamato to devise a plan to convince Hotaru to accept their protection. Using his unique jutsu, Sai drew mountain leeches to fall on Hotaru, who freaks out and becomes afraid, causing her to accept Team 7's protection. When they reached the village, Team 7 leaves Hotaru with the Tsuchigumo clan and Hotaru thanks Naruto before he leaves. When Naruto left he saw the look on the peoples faces back at the clan's village, so he decided to return to check things out.

Source: naruto.wikia.com