Amaumi Haruhiko is a high school student who attends Shimano Academy in a town called Narasakicho. Narasakicho contains an unknown rainbow which constantly overlooks the town and is related to granting a magical wish called "Gift". Gift is a once-in-a-lifetime present between two people. As a child, Haruhiko has been close with his childhood friend, Kirino, until he obtains a new non-blood sister by the name of Riko. Haruhiko develops a strong relationship with Riko until they sadly depart due to the fact Haruhiko's father could no longer support the two of them. After some times passes by, Riko finally returns to the town of Narasakicho, and along with Kirino, starts to attend Shimano Academy with Haruhiko. The series revolves around the relationship among these main protagonists and slowly reveals the story behind both Gift and the rainbow.
Haruhiko Amami
Riko Fukamine
Kirino Konosaka
Chisa Fujimiya
Rinka Hokazono
Yukari Kamishiro
Masaki Edo
Nami Sato
Soichi Amami
Ibuki Yajima
Miho Kikuchi
Tamami Konoe
Sena Asakawa
Nene Himekura
Miyu Akihara
Haru Amami
Kasai
Sakaguchi
Maiko
Ayako
Haruhiko's childhood friend Kirino had been eagerly awaiting the day that they'd once again be able to attend school together, but a misuse of Gift's mysterious power threatens to ruin the entrance ceremony.
Riko, Haruhiko's younger sister, returns home after several years. Things start to return to the way they once were, but what of Kirino's feelings?
Haruhiko is getting jealous that other guys are looking Riko's way, but why should he have these feelings if he's only her brother? Does Riko even see him that way?
On a hot summer day, Maki and the others invite Haruhiko and Riko to the beach. While there, he devises plans to get Haruhiko and Riko back on better terms.
Nami won't leave Rinka alone, so Rinka and Haruhiko pretend to be a couple in the hopes that she'll back off. Nami sees through their ruse and unleashes the terrible side of Gift's power.
Kirino is having misgivings about Haruhiko and Riko finally making up. As an unintended consequence of a witch's fake Gift, Haruhiko begins to see Riko as his late mother.
Haruhiko finds the witch responsible for the fake Gifts and discovers that she is, in fact, Chisa. In order to see Riko as herself again, Haruhiko is prepared to sacrifice some very important memories... and even the rainbow itself.
While on a school trip in Kyoto with Riko and the others in his class, Haruhiko finds himself unable to buy the love charm Kirino had requested, because his feelings lie elsewhere.
Upon returning from the trip, Haruhiko admits to Kirino that he can't return her feelings. She later accuses Riko of breaking an important childhood promise.
With Riko begging for forgiveness, an emotionally-broken Kirino has Riko give up her past with Haruhiko so she can stay with him from now on. Haruhiko is then forced to come to terms with his own severed past with Kirino.
Haruhiko struggles to come to terms with Gift's true power and how he can protect the one he loves, which leads him back to the very first Gift: a parting farewell from his dying mother.
With Riko's memories restored, Haruhiko sets about repairing his broken friendship with Kirino. Though Gift's power is gone, and the Eternal Rainbow along with it, Haruhiko and Riko vow to see the rainbow together again.