When Sasuke finally enters the ANBU, he spars only with Kakashi. Mo one else will risk going up against him, sword to sword--he has worked for six strange and turbulent years now in Leaf's service, but stigma still trails from him like ribbons. He accepts it, because there is no one with whom he would rather spar.
When his sword flashes through the air, with only Kakashi's weapon there to counter it, it is as if the two of them are slicing the lies from him. His world narrows, and in that perfect silver blur he knows many things that he barely dares to admit any other time--
--Kakashi is better than him, unconquerable. Sasuke has become stronger than him, true, but there are ways in which his teacher will always be better, always be the one in charge. He strains against this truth like he might bite down on a sore tooth. In time the pain becomes an intoxicating comfort.
--he needs someone else's sword to block his, to send it spinning with a sharp clash. Naruto and Sakura will tear at him with their claws and their love, and he needs that too, but they will not, cannot, stay his sword and say, "This is where you stop."
--in some places he is still broken, nigh unfixable, but that is all right, because Kakashi is broken too.