After the death of his grandfather, 19-year-old Kazuya Souma—an aspiring civil servant—is left all alone with no one to call family. Out of the blue, he is transported to the Elfrieden Kingdom, a small ailing country in another world, to be a hero. An ongoing war with the demon army has put the entire world in peril, and Kazuya was summoned to aid in the conflict as an offering from Elfrieden to its allies. Dissatisfied with being used as tribute, Kazuya decides to help the kingdom revamp its declining economy—not by way of adventuring or war, but through administrative reform. Abruptly declared the King of Elfrieden and betrothed to the princess, the Realist Hero Kazuya sets out to assemble a group of talented citizens who will assist him in his bureaucratic battles to get the kingdom back on its feet.

Together with his talented aides, the Realist Hero Kazuya Souma continues his quest of reinvigorating the Elfrieden Kingdom through administrative reform. Having successfully conquered Van—the capital city of the Principality of Amidonia—Kazuya now faces the envoy from Gran Chaos Empire, who wishes to impose punishment for breaching the ban on war established by the Mankind Declaration Treaty. Despite the dire situation, Kazuya sees a path to avoid unnecessary conflict whilst gaining new allies. With his plan being seemingly perfect, the only barrier to success is gaining approval from the envoy.

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.

Figure skater Tazusa Sakurano is on the fast track to the Olympics. As a top contender, her chances rest on a single competition in Canada. However, during her program, she falls and hits her head on the ice, knocking her unconscious. At the same time, Canadian stunt pilot Pete Pumps goes down in a fiery blaze. After her devastating failure, Tazusa returns home to Japan, but she starts hearing a voice in her head. In reality, when Pete had arrived at the gates of heaven, he was denied access for his sins. Instead, he was told to wait 100 days and is now trapped in Tazusa's body! Unwilling to let this interrupt her life—even if her body is a bit crowded—Tazusa moves forward with skating, all while a pesky voice may just be able to help her achieve her dream.