In 2020, cheerful high school student Aida Asumi leads a second life inside the online fantasy role-playing game The World R:X under the name Sakuya. With her classmates Ikuta Iori, who plays as Tobias, and Etou Eri, who plays as Mary, she sets out to beat The One Sin, a dungeon said to be impossible to conquer. The three lose their way in its maze and end up trapping other guild members by accident, while a mysterious cat watches their mistake unfold. Whether it is another player or an NPC is unclear. Their ordinary treasure hunt takes an ominous turn after a bad run-in with an elite guild and a strange player named Hermit, when Eri falls unconscious and, for reasons no one knows, cannot wake up. The three-episode OVA mixes action, adventure, fantasy and science fiction.