Official dossier
Arisa Kato is Reona’s best friend, voiced by Natsumi Haruse. She attends Koin Girls’ Academy, a prestigious school, and her life is described as the opposite of Reona’s. The two still spent time together regularly.
When the mall they were visiting anomalized, Arisa’s whereabouts became unknown. The official site does not say what happened to her beyond that.
Narrative role
Arisa is the reason the story exists: Reona’s dive career, her return to the zones, and her refusal to stay out are all tied to finding her. She is also the emotional counterweight to the office’s institutional language.
Because the official files stop at “missing”, this archive does not publish theories about her fate as fact. Any page that does is speculating.
Where to look for updates
The official site and the game itself are the only sources that can resolve Arisa’s story. This page will be updated if the official material adds a confirmed detail.
Spoiler policy: this page avoids late-game content by design.
Anomalith Archive. “Arisa Kato: the friend who disappeared.” Last updated 2026-10-29. https://anomalith.net/lore/arisa/