Roar and Howl! The Ultimate Tag-Team!

is episode 120 of the original Naruto anime.

Synopsis
As Tayuya guides her three Doki after Shikamaru, she activates the first level of her cursed seal to make controlling them easier. Naruto too begins his battle, creating a great deal of shadow clones with which to attack Kimimaro, though Kimimaro is able to defeat the clones by the dozens. As the fight between Kiba and Akamaru vs. Sakon and Ukon rages on, Ukon pushes his cursed seal into its second level. Recognizing the huge increase in strength that this allows the brothers, Kiba and Akamaru combine to become a giant double-headed wolf. The combined beast charges towards Sakon and Ukon, though the brothers are able to block the attack. As the wolf transformation disperses, Akamaru is attacked and left heavily injured, and Ukon merges himself with Kiba's body. Needing to get rid of Ukon to save Akamaru, Kiba stabs himself in the stomach, causing him and Ukon to start coughing up blood.