I’ve been seeing posts saying that the ending was just Tae Sul’s dream, that everything that happened never really happened. However, I feel like it wasn’t a dream.
Just like the title “Sisyphus: The Myth,” which is a myth about repetition, I think the ending was just one of those “repeats.” The ending where Sigma was holding a notebook where everything that happened was written kind of confirms that the time travel did happen. Han Tae Sul telling Seo Hae to find him before they met also hints that Seo Hae probably got to use the uploader, and was probably the only person who got to use it once. This means that Seo Hae probably traveled back in time.
My theory is that — since Han Tae Sul can code and create an uploader that can only be used once — either one of them probably sent a message for their future selves to see. Thus, Seo Hae probably looked for Tae Sul, and he probably created an uploader solely for Seo Hae’s use. Seo Hae’s diary can also be one of the reasons why this happened, the young Seo Hae probably got her diary. His father also probably told her about Tae Sul, since he might also want the two of them to have a happy ending.
Regarding the possibility that Seo Hae is Han Tae Sul’s hallucination, I feel like it’s not a hallucination, but I understand why this seems possible. One of the reasons why I think Seo Hae is real is because he never got to touch his brother when he was hallucinating, but got to touch Seo Hae, which may confirm that this is his reality. There are also theories about Han Tae Sul and Sigma having mental issues, but it’s impossible that they have the same and very detailed imaginative scenarios about the Control Bureau, Asia Mart, the uploader, etc.
Another reason why this can really be about time travel is because the Myth of Sisyphus is about cheating death (which is what happened to Tae Sul before he decided to end his life) and being punished via a repetition quest (the boulder in the actual Myth of Sisyphus represents this).
Also, for the deaths, it was their future selves that died and faded away. But their past/present selves are still there, they are pretty much still alive in that timeline. Hence, whatever happened to their future selves will not affect their past selves. Their past selves’ lives restarted and they are then able to create a new future.
What do you guys think? This is my personal take. Though, I feel like there are a lot of different ways to interpret the ending of this series.
UPDATE: Another theory by Carissa Cestina is that Han Tae Sul did something to the uploader so that their past selves would end up sitting together during a flight. This makes a lot of sense since Han Tae Sul and Seo Hae’s memories are intact.
Adding to this theory… there might be a possible loophole since the two still need to go back to the exact same time period to kill Sigma. However, they no longer need to do this. Even if killing Sigma’s future self will not affect the one in the past that they faced in the church, they don’t need to travel to the same timeline to kill Sigma. This is because the evil time traveler Sigma will no longer exist since he changed already due to Seo Hae’s father’s kindness.
NOTE: Also, I created a timeline explanation that also explains the repetition part: