Paradox: Sign-In Across Two Worlds

Neolan died at the hand of an Unknown Demon, his heart getting pierced and crushed by it while regret and rage fill his fading consciousness for not being able to save anyone he loved, nor the world he had fought for until his final breath.

But what happens after his death shocks him to the core.

He reincarnates in a body that wasn't his own, in a completely different world where Cultivation exists and the path to becoming stronger is completely different from everything he knew.

Fortunately, he awakens a cliche type of Sign-In system known as the Paradox Sign-In System, which has a simple rule.

Sign-In once every 24 hours and receive a completely random reward.

With his memories from his previous life and the System now in his hands, Neolan begins adapting to this new world while trying to understand what happened to him.

But then he sees something that should never have existed in this world.

Demons.

The same Demons that destroyed Earth.

Before he could find the answers, he seeks, his first 24 hours in this world finally came to an end.

And the System displayed a message that leaves him stunned.

[24 hours have passed. Host will now be transferred to Earth.]

That is when Neolan realizes the truth.

He hadn't simply reincarnated into another world.

He had regressed back in time in both worlds.

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Extra tags: Cultivation | System | Transmigration | Reincarnation | Apocalypse | Overpowered Protagonist | Strong Protagonist | Multiple Worlds | Dual Systems | Sword master | Demons | Survival | R18 | Dimensions/Realms | Awakening | Regression

[Warning: There will be explicit scenes in the future, read on your own terms, you can skip them if you want]