Sword Art Online: Why Were Kirito & Asuna’s Memories Erased After Leaving Underworld?

gamerant.com:

Sword Art Online revolves around the concept of transferring one’s consciousness to virtual reality worlds to embark on thrilling adventures. The main characters, Kirito and Asuna, who are romantically attached, witness a huge change in this during the Alicization Arc.

The plot changes, focusing on Kirito's exploration of the new VR world he encounters and Asuna's quest to find her beloved. Luckily, due to a couple of fortunate events, the duo are reunited and spend a long time together, reaching up to 200 years.

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Towards the later part of Sword Art Online: War of Underworld, a situation arises, forcing Asuna and Kirito to stay in the Underworld to aid Alice’s escape from the VR world to the real world. As a result of their choices, they spent 200 years in Underworld, a situation caused by VR’s reboot. The 200 years they spent in Underworld were attributed to Fluctlight's technology effect; time acceleration. After Kirito and Asuna leave the Underworld after 200 years, they decide to remove their memories of the VR world.

Many SAO fans were puzzled at their decision, but Asuna and Kirito made their decision with good reason. Regarding the Fluctlight's acceleration, time was manipulated unusually. In short, Fluctlight's technology caused time to speed up by 1000 times compared to the real world’s time flow. Asuna also decides to stay with him, since earlier on in the Alicization Arc, Kirito was trapped alone, away from his friends, lover and family. So, Asuna convinces Kirito that they can spend even a thousand years in the Underworld together. Kirito and Asuna vow to remember Alice and her friends, waiting for them in the real world. Surprisingly, after leaving the Underworld, Kirito