The Oto Four (音の四人衆, Oto no Yoninshū) is chapter 177 of the Naruto manga.
Kakashi ties Sasuke to a tree so that he can speak to him without running off. Kakashi advises Sasuke against his pursuit for revenge against Itachi. Sasuke retorts that Kakashi doesn't know what he's been through and offers to kill everyone Kakashi loves. Kakashi points out that everyone he loves is already dead. However, both he and Sasuke have found friends in Team 7, and they would do well to value what they still have more than what have lost. Kakashi leaves him to consider it and he struggles to forget about Itachi. Before he can reach a conclusion he is attacked by the Sound Four. He quickly repels them and challenges them to try again.