"Gift - eternal rainbow" is 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 returns to his hometown after several years away. He reunites with his childhood friends, including Riko Fukumine, Kirino Morishita, and Chisa Mizuhara, all of whom attend the local school, Kibougaoka Academy. The town's unique "Gift" phenomenon grants certain individuals the ability to bestow a single wish upon someone else, but the mechanics and limitations of this power remain shrouded in mystery.

Haruhiko's return coincides with the arrival of a new transfer student, Riko Fukumine, who harbors a deep connection to him from their shared past. As the narrative unfolds, it becomes clear that Riko possesses a Gift, though her motivations and the nature of her wish are initially unclear. The story explores the relationships between Haruhiko and the girls, particularly Riko, Kirino, and Chisa, as they navigate their feelings, memories, and the implications of the Gifts they hold.

Kirino Morishita, Haruhiko's childhood friend and neighbor, is a cheerful and energetic girl who harbors unspoken feelings for him. Her Gift becomes a focal point as she struggles with the emotional weight of her wish. Chisa Mizuhara, another close friend, is more reserved and introspective, often acting as a stabilizing presence within the group. Her Gift ties into her desire to protect those she cares about, even at personal cost.

The narrative delves into themes of love, sacrifice, and the consequences of wishes, as the characters grapple with the ethical and emotional dilemmas posed by their Gifts. The town's history and the origins of the Gift phenomenon are gradually revealed, adding layers of intrigue and complexity to the story. The interplay between the characters' personal struggles and the supernatural elements of the Gifts drives the plot forward, culminating in a resolution that ties together their individual arcs and the overarching mystery of Narasakicho.

The series balances moments of lighthearted humor and heartfelt drama, with a focus on character development and interpersonal relationships. The central romance, particularly between Haruhiko and Riko, is a key narrative thread, but the story also gives significant attention to the bonds between all the main characters. Through its exploration of wishes and their consequences, "Gift - eternal rainbow" presents a thoughtful examination of human desires and the impact of choices on oneself and others.