What is the Zero Requiem?

The Zero Requiem is Lelouch's final plan — a coordinated sacrifice designed to achieve world peace by directing all the world's hatred toward Zero (Lelouch) and then killing him. With hatred focused on a single villain who is then destroyed, nations that had been at war unite in celebration and resentment toward each other dissolves. Lelouch seizes control of the entire world as Emperor, commits atrocities extreme enough to make himself the universal enemy, then has Suzaku (disguised as Zero) assassinate him publicly.

Why did Lelouch need to die for it to work?

Because the hatred had to be real, and it had to end. If Lelouch continued existing, he remained a threat to unite against. His death as Zero, executed by what looks like a freedom fighter, ends the cycle. Nunnally and the world cry for Zero while mourning the Emperor they hated — without realizing they're mourning the same person.

What makes the Zero Requiem emotionally devastating?

Lelouch dies knowing Nunnally (whom he built the entire revolution to protect) now hates him. Suzaku survives but gives up his identity permanently — becoming Zero forever, carrying the guilt of executing his best friend. Lelouch's final moments include Nunnally taking his hand as he dies, and the realization that she loves him — the one thing he spent the series believing he couldn't have.

Does Lelouch actually die?

In the original anime: ambiguously. There's a famous theory that Lelouch, having taken Charles's Code, became immortal and appears as a cart driver after the finale. This is deliberately left unresolved. Code Geass: Resurrection (2019) confirms he survived and was resurrected — but this is considered separate from the original ending's intent.

What does the Zero Requiem teach about sacrifice?

That the most complete sacrifice is one where you can't be praised for it. Lelouch cannot tell Nunnally, cannot be remembered well, cannot be mourned as a hero. His goodness dies with his reputation. This is both noble and heartbreaking — and exactly what he chose.