When word spread across the continent that the second Uchiha survivor had become the Hidden Villages Era's second sage after Jiraiya the Gallant, even Itachi found himself uncertain how he ought to handle Danzō's orders to eliminate this seemingly inoffensive girl, now an existential threat to the village's power structure. Sakura was perhaps one of the Uchiha clan's strongest members in history, and a master of senjutsu to boot!
And so, Itachi studied Sakura's mission records. Her talent in genjutsu was off the charts, and she was a ninjutsu genius who had mastered all five nature transformations. Her taijutsu wasn't atrocious either; she knew all of Tsunade's moves, which also meant she was an undying, endlessly regenerating monster who could split mountains and shatter bones with a mere wave of her hand.
How, then, was his dying self supposed to accomplish such a miracle?
Outwardly, Sakura had few weaknesses, but there was no such thing as a perfect shinobi.
According to Danzō's intel, she had awakened the same eye technique once possessed by his old friend Shisui, which made it disturbingly easy for Itachi to read her true nature and construct a precise profile of her. If their eyes were the same, then the soul behind them would not differ by much… and Itachi knew Shisui very well indeed.
Sakura cared too deeply for her comrades, could be scatterbrained at times, and disliked both pain and inflicting it. Yet, paradoxically, she was something of a battle junkie: she thrived on devising strategies mid-fight, matching wits and testing her strength against her opponents.
What did that tell Itachi?
Even if Sakura didn't do it consciously, she had a habit of looking down on those she deemed beneath her, and she was merciful as well— and from the moment she became a sage, she had risen far beyond the reach of ordinary shinobi.
Everyone was beneath her transcendent self, so she would underestimate everyone.
And so, Itachi decided to simultaneously target her greatest strength and deepest weakness; he would engage her in genjutsu when she least expected it… and at the same time, he would implant her dear friend Naruto with his backup plan, in case he failed to eliminate Sakura outright.
Itachi had forced a crow imbued with Shisui's Kotoamatsukami down Naruto's throat, coded to respond solely to Sakura's eyes' chakra. If she ever turned against the Hidden Leaf, the genjutsu would compel her to forget about vengeance, and in turn, compel her to subjugate Sasuke with her own Kotoamatsukami.
But that was only a contingency; the true plan was to implant an engraved Tsukuyomi in Naruto's eye. When Sakura inevitably stopped on the way to the Uchiha Hideout to dispel the genjutsu afflicting her friend Naruto, she would unknowingly get infected by a mind virus!
And finally, when the battle tipped in Sasuke's favour, this implanted genjutsu would activate, erasing Naruto's and Itachi's chakra signatures from Sakura's perception; it was a powerful illusion, but a very subtle one too, extremely difficult to notice at first. This Tsukuyomi existed for a single purpose: to create an illusionary world identical to the real one where neither of them existed… and it was that very subtlety that would prove her undoing!
"ITACHIII!" Sasuke roared.
Sakura turned around, looking around wildly for Itachi, but he had slipped into the gap between perception and reality. No matter how hard she used her senses, she was mentally incapable of registering his presence!
Indeed, everything was unfolding exactly as Itachi had planned. His psychological profile of Sakura was flawless… but there was one variable he could never have accounted for: she had never looked down on him for even a moment, because he was, quite simply, the G.O.A.T. of the Naruto series.
In the split second before Itachi's blade would have taken her head and the black flames of Amaterasu reduced her remains to ash to stop any chance of regeneration, Sakura found herself wondering why she hadn't sensed Naruto activating the Ame-no-Uzume she had implanted in his eye, should he ever face mortal danger.
Then, catching the panic in Sasuke's eyes, though she hadn't the faintest idea what was happening, Sakura knew something had gone dreadfully wrong. Her scarlet eyes flared, power surging outwards and pink chakra wreathing her body as she mustered the strongest defence she could think of.
"Susano'o!"
The chakra construct's ribs expanded rapidly around her, tearing Itachi out of the cognitive gap where he'd hidden himself and blasting him away, sending him rolling across the floor of the Uchiha hideout.
"Sakura?" Sasuke breathed, staring in disbelief as the pink chakra surrounding her swelled, rising higher and higher. "Is that… your true power?"
A laugh filled with madness rang out. Sakura and Sasuke glanced at Itachi, who was pushing himself to his feet, clutching his face with a clawed hand.
"To think a half-breed could develop her Uchiha bloodline to this extent!" Itachi shouted giddily. "Your eyes are mine, mine, mine!"
Sakura's Susano'o was still growing. The chakra construct had formed a skull and a pair of arms, with illusory muscles and sinew blooming along its bones. It could no longer fit inside the building; the hideout was collapsing, chunks of rock, plaster, and brick tumbling down as the Susano'o's head pierced through the ceiling.
"Ngh…" Sakura groaned, holding up a hand to her bleeding eyes.
"How fitting for an ending," Itachi laughed. "We'll clash with the Uchiha clan's ultimate technique… Susano'o!"
Orange flames roared to life around Itachi, lifting him within a whirling firestorm that coalesced into the shape of an armoured tengu wearing a horned helmet. His Susano'o's growth quickly surpassed Sakura's, towering over her pink construct with domineering might, longsword and shield in hand.
"Sasuke!" Sakura cried out.
At this rate, he would be squashed underfoot in the melee!
Any semblance of reason and logic evaporated from Sakura's brain. Blood streamed from her eyes as she screamed and forced her Susano'o to keep pace with Itachi's. The pink chakra construct's chest swelled in two places; armour formed over its unmistakeable curves; a gleaming breastplate that concealed any important bits before they appeared.
A flowing hakama unfurled beneath the armour, cloaking its legs, and a conical straw hat adorned with twin demon horns took shape atop its head. The straw hat's rim was drawn low over its head, obscuring the face beneath in shadow… save for two ominous eyes that blazed like twin torches in the dark of night.
Sakura reached out, and the Susano'o's gigantic yet slender arm mirrored her movement, plucking Sasuke by the scruff of the neck before tucking him inside her breastplate, where he hung helplessly, suspended within the chakra forming the Susano'o's right breast.