Sisyphus — Ending Explained

The narrative hinges on several critical revelations and climax twists:

• Han Tae-san's Survival: Tae-sul's older brother did not die a decade ago; he uncovered the advance infiltration from the future and hid in temporal stasis and shadows to shield Tae-sul.
• The True Identity of Sigma: Sigma is revealed to be Seo Won-ju, a bullied elementary school classmate of Tae-sul who survived the nuclear strike in a shelter and used future knowledge to establish an advance syndicate in the past.
• The Control Bureau's Corruption: Rather than a legitimate state agency, the Control Bureau was infiltrated and commandeered by Sigma's temporal syndicate to collect advanced technology and execute timeline disruptors.
• The Diary Bootstrap Paradox: Seo-hae's guiding diary was written by her older self during previous failed loop iterations and buried by her mother's grave to guide her younger self in an ongoing causal chain.
• The Climax Paradox: In Episode 16, Tae-sul outwits Sigma during the church confrontation, leading to Sigma's demise. However, when his close friend Eddie Kim prepares to force the Uploader's completion out of jealousy and obsession with Seo-jin, Tae-sul realizes the machine will always be built as long as he lives. Tae-sul shoots himself, extinguishing the inventor and preventing the Uploader's creation. Consequently, future Seo-hae dissolves, the nuclear apocalypse is erased, and billions of lives are saved.

Interpretations of the series finale diverge across three primary readings:

• The Broken Loop and Quantum Afterlife (Canonical Sci-Fi Reading): Tae-sul's suicide represents the ultimate unpredictable variable that terminates the causal chain. Because the Uploader is never completed, the nuclear war never happens, future Seo-hae dissolves, and the final airplane scene depicts a metaphysical afterlife where their souls exist peacefully outside of spacetime.
• The Hallucinatory / Dying Consciousness Reading: Proposes that Tae-sul never survived the catastrophic mid-air plane crisis in Episode 1. The entire narrative is interpreted as his brain's dying neural sequence attempting to resolve survivor's guilt over Tae-san, concluding with him returning to the cockpit seat at the moment of death.
• The Incomplete Sisyphean Cycle (Sinister Loop Reading): Highlighted by the final glimpse of young Seo Won-ju still harboring darkness in his sketchbook, suggesting that defeating one Sigma does not purge human cruelty, and that humanity is doomed to push the apocalyptic boulder up the mountain again in another iteration.