Kakashi was aware of Itachi rom the moment the Uchiha entered ANBU. There was an aspect of pride in his notice of the younger nin -- Kakashi himself had been hailed as a young genius for almost all his life. His promotion to jounin and subsequent entery into ANBU had been delayed, though, due to the... issue... with his father.
To enter ANBU at fifteen was still impressive, though, and Kakashi had attracted quite a bit of notice when he had. As much as he tried dto act as though it were below him to notice such things, as much as he tried to pretend that he was nothing more than another shinobi, closed off and hard and not needing such things as recognition for his accomplishment, he still ate it up when people did notice, when he got just a little extra praise for doing well. It was... something.
And then it stopped, because Itachi entered ANBU, and suddenly he was the new darling. "The Uchiha genius," people called him, and Kakashi faded into yet another member of the faceless ranks of Black Ops.
He would never admit it was jealousy. If anyone noticed his wariness of the younger nin, they most likely assumed it was just a remnant of the issues he'd had with the Uchiha after he'd returned from the bridge mission less a teammate and plus a new red eye.
--
He was assigned to the cleanup crew that handled the Uchiha district in the aftermath of the massacre, and he was rather unsurprised by what had happened. Not that he had been expecting Itachi to kil everyone who shared his blood, save for the little boy who was currently under intensive treatment at the hospital for the aftereffects of the jutsu used on him, as well as the chock and mental trauma of finding his entire clan annihilated. He'd expected something, though. Scuttlebutt around ANBU and his own observations of their missions together had been that Itachi had been brooding quite often of late, and occasionally they'd been unable to find him when needed. He'd missed briefings. Very nearly been late for missions.
To Kakashi, and most likely to others of ANBU as well, those were danger signs. The Sharingan came with an inherent risk of mental instability, a byproduct of the consanguinity that was required to keep the bloodline limit a dominant trait of the Uchiha, and Kakashi knew that the risk had been multiple by Itachi's young start, by ttthe intense pressure to succeed he had been under. And ANBU... ANBU was not a place for children. Fifteen was young to enter. To become a member of the elite corps, to be snt on the darkest, most soul-killing missions, at eleven years of age, and to complete them with the cold efficiency Kakashi had seen from Itachi in their missions together.... down that road lay madness, and madness had indeed come home to roost.
As he and the rest of his unit combed through the district, looking for any clues about what might have set off the Uchiha genius, or any evidence of where he might have fled to, Kakashi looked at the slaughtered bodies of all the clan members -- shinobi in their prime, civilians who had never held a kunai in their lives, the elterly who might once have been warriors but now posed little threat to anyone, children cut down before they could have a chance to blossom -- he wondered if Itachi had blamed his entire clan for his fast rise, for exposing him to the pressures of ANBU at far too young an age.
An infant, no more than a month or two old, was slit from belly to throat. He stared at the ruined little body and shook his head.
--
He had not thought overmuch about Itachi in the intervening years, not until that sole survivor of the massacre wound up on the first time to pass the bell test. The traumatized little boy he remembered from the reports had grown into a closed-off, bitter preteen -- hardly surprising. But Kakashi was very gratified to note that Sasuke, while intelligent, didn't show any signs of the same level of destructive genius his brother had manifesed. The poor kid didn't need any help getting further into the 'at-risk' category he was already in.
Memories of the bloodbath in the Uchiha district made Kakashi concentrate on Sasuke, at times to the exclusion of his teammates. While he hadn't been particularly fond of Itachi even before the massacre, he didn't want to see Sasuke go down the same road, and it seemed all too likely, given that the pressures of being a genius were probably less than the mental trauma of having been caught in said genius' bloody breakdown.
Having Orochimaru sniffing around didn't exactly help matters, either.
And then Itachi reappeared in the village, and Kakashi found out the hard way that having gone at least temporarily insane hadn't dulled the man's skills any. The sense of competition he'd had back in those early days, when Itachi had overtaken his spotlight as the young genius of ANBU, reasserted itself and he spent the days after the encounter, trapped in recovery from the Tsukiyomi, quiet and closed-off, smarting fro mthe easy defeat and determined to find a way to get the Mangekyou for himself. He was not a blood Uchiha -- he had no idea if he could even do it. He'd gained the third tomoe, though, and if he could evolve the Sharingan a little, he should be able to evolve it a lot.
He would not let Itachi do that to him again.
--
He got the Mangekyou, al right -- and some selfish part of him was relieved that Naruto and Sakura had both found other teachers, so he ould focus hiself on that obsssion until it was completed. But he never had a proper chance to use it against Itachi, to test himself and see if he could finally put him in his place as he'd been longing to do since Itachi was eleven and newly in his mask.
In the middle of the fight against that... that strange someone, he hadn't fully had the time to appreciate what it meant, that Sasuke had won and Itachi was dead. It wasn't until they returned to Konoha and Naruto stopped brooding over having missed Sasuke that it really sank in -- Itachi was dead.
Either there had been a tremendous upset -- and that was unlikely, he knew -- or Sasuke had legitimately outclassed his brother. And that... that was a disturbing thought.
Kakashi rubbed his Sharingan eye and wished he'd never heard the name Uchiha.