Bushy Brow's Pledge: Undying Love and Protection!

is episode 31 of the original Naruto anime.

Synopsis
Rock Lee leapt through the trees, after having split up with his team-mates to try to find the other scroll they needed. While hiding under a tree, Sakura tended to Sasuke's and Naruto's wounds, trying to stay awake herself. She then dreamt of the two waking up, with Orochimaru then turning into a giant snake and eating the two of them. When she woke, she heard something rustling in the bushes. A squirrel came out, but Sakura threw a kunai towards it, sending it away, while Dosu Kinuta, Kin Tsuchi, and Zaku Abumi wondered if she had seen the explosive tag that they had put on the squirrel's back. They then prepared to attack.

While Rock Lee stopped on a branch, some leaves began to fall. He said to himself that, if he could catch all 20 leaves before they hit the ground, Sakura would fall in love with him. After catching 19 of the 20 leaves he saw a squirrel with an explosive tag on its back, and saved it before destroying the explosive tag, letting the last leaf hit the ground. Neji ended up finding Ino, Shikamaru, and Chōji hiding behind some bushes, and so they moved onto plan 2, in which Ino tried her hardest to seduce Neji but failed, and he left without taking their scroll. Dosu and his squad challenged Sasuke, but she defended him and set off two traps at them. The enemy team saw through the first one, but didn't see the second one coming.

Unfortunately Dosu managed to destroy the trap with ease, and shortly after that made a remark about how Sakura had no right to be a ninja. Just before they could land their attack, however, Rock Lee showed up and knocked the three of them away. Sakura wondered why Rock Lee was there, to which he declared that he would protect her until his death. Dosu tried to attack Rock Lee, but Lee managed to pull up a root to block the attack with. Rock Lee remembered back to when he had learned the Front Lotus, and how, when he had finally mastered it, that his sensei, Might Guy, had told him that it was forbidden. Guy had explained that that jutsu put tremendous strain on a person's muscles, and that it brought power that over exceeded the limits a person's body could take, and thus it should only be used to protect the life of someone precious.

Lee then unwrapped some of his arm bandages and attacked Dosu, but Zaku managed to help him avoid the attack, with Lee's body still not recovered from the jutsu.