"Gift ~eternal rainbow~" is a 12-episode anime series set in the fictional town of Narasakicho, a place known for its frequent rainbows and a mysterious phenomenon called "Gift." The story revolves around Haruhiko Amami, a high school student who lives with his childhood friend, Riko Fukumine, and her younger sister, Kirino. Haruhiko is a kind and easygoing individual, but his life takes a turn when his childhood friend, Chisa Mizuhara, returns to town after several years of absence. Chisa, who had moved away due to family circumstances, harbors unresolved feelings for Haruhiko, which complicates their reunion.

The central plot involves the concept of "Gift," a magical ability that allows individuals to grant the deepest wishes of others. This power is tied to the town's legend of the eternal rainbow, which is said to appear when a true wish is fulfilled. Haruhiko becomes entangled in the lives of several girls who possess the Gift, each with their own emotional struggles and desires. Among them are Riko, who hides her feelings for Haruhiko behind a cheerful demeanor; Kirino, who looks up to Haruhiko as a brother figure; and Chisa, who struggles to reconcile her past with her present feelings.

As the story progresses, Haruhiko helps each girl confront their personal challenges, often using the Gift to bring closure to their emotional conflicts. However, the use of the Gift comes with a cost, as it can only be granted once per person, and its misuse can lead to unintended consequences. The narrative explores themes of love, sacrifice, and the complexities of human relationships, as the characters navigate their intertwined fates and the mysteries of the eternal rainbow.

The series balances lighthearted moments with emotional depth, focusing on the bonds between the characters and their growth throughout the story. While the romantic elements are prominent, the anime also delves into the broader implications of the Gift and its impact on the town's inhabitants. The resolution ties together the characters' arcs, culminating in a heartfelt conclusion that emphasizes the importance of understanding and fulfilling one's true desires.