A brother and his younger sister-in-law live in a house where their parents are often away. Yuki, the younger sister, secretly yearns for Kenji, the elder brother. However, one night, a girl emerges from the closet in Kenji's room. Moreover, her body is transparent, and she resembles a ghost. Her name is Hiyori. She is a friend from their childhood. Although Kenji and Yuki are perplexed by the strange manner of Hiyori's appearance, they are pleased with the reunion. However, Yuki's mind is shaken as Kenji and Hiyori become intimate, and the pain in her mind from childhood is recalled. In childhood, Yuki was going to pass the light blue toy ring that Kenji had possessed to Hiyori in exchange for Hiyori's yoyo. However, because Hiyori became sick and moved away, the promise was not accomplished. Their events in childhood seem to be related to Hiyori's showing up in front of them. A painful love story of Kenji and two girls progresses.