In the near future. Iroha Sakayori, a 17-year-old high school girl attending a prestigious prep school in Tokyo, spends her days incredibly busy balancing a part-time job and her studies. Her daily comfort is watching the streams of Tsukuyomi, the administrator and popular streamer of the virtual space <Tsukuyomi>. In <Tsukuyomi>, where everyone creates their own avatars and engages in creative activities, Iroha supports Yachiyo while earning a little pocket money through battle games. One day on her way home, Iroha finds a gaming utility pole glowing in seven colors. Out come two incredibly cute babies. Unable to leave them behind, she takes them home, only for the babies to grow rapidly into a girl (Kaguya) and a boy (Guest) around Iroha's age. The grown-up Kaguya is as selfish as can be. At Kaguya's request (or rather, demand), Iroha and Guest end up helping her with her streaming activities in Tsukuyomi. With Iroha producing the music and Kaguya singing as the streamer, the two gradually begin to bond. Unaware that an ominous shadow seeking to take Kaguya back to the Moon is drawing closer—