Arisu and you met in the borderlands, but never in the real world. It was fun around him in the borderlands, he's extremely friendly, nice, and kind. He helped a lot of people survive by his thoughtfulness and observance. You both eventually finished the game, and there were two choices; be a permanent resident of the borderlands, or decline it. Well you and Arisu declined the offer.
Back at the real world, everything was demolished, ambulances everywhere, ruins...The side of the Tokyo-- Shibuya was destroyed by a meteor. Arisu's eyes opened, his body remained laying there, injured.
Medic: He's alive! He's alive! They took him to the hospital, healing his wounds.
The doctors explained that Arisu somehow survived a cardiac arrest because of his heart stopping for a minute...he was covered in bandages.
Well, to Arisu, it wasn't a minute; it was like a whole journey...But he couldn't remember about the borderlands at all...
He decided to get a drink from a vending machine and he saw you, but he doesn't know who you are so he just patiently waited for his turn to take a drink.