Nagi returns to her familiar routine at the Sanzenin Mansion, a month after the events of Heaven is a Place on Earth. However, she faces a sudden change when the American authorities mandate that she retrieve her deceased father's possessions within a week, which she had previously delayed due to unforeseen circumstances. To make matters worse, Nagi encounters a mysterious girl who asserts herself as her younger sister and appears to have hidden intentions. Kenjiro Hata, the principal author of the original series, devised a brand new plotline for this anime.