"Isekai Shōkan wa Nidome Desu" centers on Setsu, a young man who is summoned to a fantasy world as a hero, only to be betrayed and killed by the very people who called him. After his death, Setsu reincarnates back into his original world, retaining memories of his previous life and the powers he gained. Years later, he is summoned again to the same fantasy world, but this time, he is determined to exact revenge on those who wronged him.

The narrative explores Setsu's journey as he navigates the world with a mix of bitterness and resolve. He encounters familiar faces, including the princess who orchestrated his betrayal, and new allies who aid him in his quest. Setsu's powers, which include the ability to manipulate time and space, make him a formidable force, but his emotional scars and distrust of others complicate his path. The story delves into themes of betrayal, vengeance, and redemption, as Setsu grapples with his desire for retribution while uncovering deeper truths about the world and its inhabitants.

Key characters include Setsu, the vengeful protagonist; the princess who betrayed him, now a central figure in the political machinations of the world; and a diverse cast of allies and enemies who shape Setsu's journey. The plot intertwines action, strategy, and emotional conflict, as Setsu confronts his past and decides whether to destroy the world that wronged him or find a way to move beyond his pain. The series balances intense battles with moments of introspection, creating a layered narrative that explores the consequences of betrayal and the complexities of seeking justice.