Man, the idea that Itachi actually killed Sasuke and everything after is a genjutsu is one of those theories that burrows into your brain and won't leave. It hinges on the 'Tsukuyomi' being a perfect, endless illusion. The moment of the kill is the last 'real' thing Sasuke experienced, and his entire revenge arc, even the final battle with Itachi, is just a fabricated narrative inside his own shattered mind to cope with the trauma of dying.
Itachi's goal was always to protect the village by eliminating the Uchiha threat, including Sasuke. Letting him live, even manipulated, was an enormous risk. The theory suggests the real Itachi completed his mission, and the tragic hero we see later is a phantom conjured by Sasuke's psyche, a way to give his brother's cruel act a noble meaning. It makes that scene in the hallway unbearably final.
What gets me is how it reframes everything. Sasuke's power-ups, his team, his hatred—all a complex, self-punishing fantasy. The 'truth' he learns from Obito? Another layer of the delusion. It's bleak as hell, but it weirdly fits Itachi's established ruthlessness. He loved Sasuke, but duty might have truly outweighed it in that single, silent moment, making his later portrayed sacrifice a lie the audience and Sasuke both bought into. The show's actual narrative is more redemptive, but this version has a chilling, tragic logic I can't shake.
I saw a meta once pointing out how Sasuke's mangekyou pattern could be interpreted as a stylized record of that killing blow, not his brother's death. That detail stuck with me.