Coo no Sekai Renei Hayashi is just about to begin middle school and not only is she nervous about the prospect, but she continues to miss her brother who died last year. On the eve of her entrance ceremony, Renei goes to bed as usual, but when she wakes up, she finds herself in a fantastical dream world, and better still her brother is there! However, the boy she meets calls himself Coo and has no idea who she is. With no clue as to how to return home, she follows Coo to his house where his kindly mother puts her to bed. The following day, Renei wakes up back in reality and thinks that she’ll never experience Coo’s world again. However, with each following night she returns to his side and they travel the land encountering the strange and absurd as they search for Renei’s home. But is Coo’s world really just a dream, and why does Renei continue to go there night after night?