The elf mage Frieren spends a decade as part of the hero Himmel's party, on a quest to defeat the Demon King and bring peace to the world. For her companions, all humans and a dwarf, this journey represents a significant portion of their lives. For Frieren, who has lived for over a thousand years, it feels like a fleeting moment. After their victory, she casually departs, promising to reunite with them to watch a meteor shower fifty years later. When she returns, she finds her old friends aged and near the end of their lives. Witnessing Himmel's death, Frieren is overcome with a new and painful emotion: regret for not having truly gotten to know him during their time together.

The story follows Frieren on her second great journey, one not of conquest but of connection. She travels north toward the demon king's former castle, a place called Ende, hoping to find a way to speak with the dead and properly say goodbye to her old comrades. To atone for her past emotional distance, she takes on an apprentice, a young human mage named Fern, who was raised by the late priest Heiter. They are soon joined by Stark, a timid but powerful young warrior trained by the dwarf Eisen. Together, this new party retraces parts of the old hero's journey, visiting familiar villages and encountering lingering threats.

The setting is a fantasy world recovering from a great war, where the remnants of the demon army still pose a danger. Early narrative arcs establish the party's dynamics and Frieren's immense power. The story introduces a formidable demon, Aura the Guillotine, who commands an undead army and forces Frieren into a desperate magical duel. Later, the party enters the northern lands and must navigate the political landscape of the Continental Magic Association, leading Frieren and Fern to participate in a rigorous first-class mage exam. This arc introduces a wide cast of ambitious and eccentric mages, each with their own philosophies on magic. Throughout these adventures, flashbacks reveal how Himmel's seemingly small, kind actions in the past continue to shape Frieren's understanding of humanity in the present.