Kakashi, My Eternal Rival!

is episode 241 of the Naruto: Shippūden anime.

Summary
In Konohagakure, Kakashi, while meeting with Tsunade about the impending war, receives an emergency messenger tortoise from Guy with an SOS message, so he heads out to find out what has happened. On board the ship, Guy recalls the time when he and Kakashi first became rivals and their numerous battles since then. Later on in the night, the jōnin meet where Yamato tells them about a rumour of a shinobi capable of not only copying someone's appearance, but also their chakra. Kakashi soon arrives at the ship, and calls for Guy. Unaware that he sent an SOS message, Guy comes to the conclusion that the one before him could be one of those imposters that Yamato spoke of. With this notion Guy proceeds to attack Kakashi and later Aoba and Yamato when they side with Kakashi. After giving Guy irrefutable proof that he was who he said he was by telling him something from their youth, Kakashi returns to Konoha upon learning that the SOS tortoise was sent by accident.

Trivia

 * In this episode, Naruto can be briefly seen wearing the First Hokage's necklace although it had already been destroyed in the fight against Pain.