Frieren is the protagonist of her story, a mage who belongs to the elven race and is over one thousand years old. Her long lifespan has given her a perception of time that is fundamentally different from that of humans, often causing her to view periods of decades as fleeting moments. This characteristic is central to her identity; she appears young despite her age and possesses a calm, stoic demeanor that can be mistaken for aloofness or emotional coldness.

Frieren's background is steeped in loss and a longstanding conflict with demons. Over a millennium ago, her home village was destroyed by demon forces, an event from which she was saved by the great mage Flamme. This encounter instilled in her a deep-seated and lifelong dedication to eradicating demons, eventually earning her the feared moniker "Frieren the Slayer" as she became the mage known to have buried more of their kind than any other in history. Centuries later, she joined the hero Himmel's party, embarking on a ten-year quest that culminated in the defeat of the Demon King. After this journey, the party disbanded, and Frieren went on her separate way.

The primary catalyst for Frieren's role in the story is the death of her former companion, the hero Himmel. Reuniting with him and the rest of her old party fifty years after their adventures, she finds them significantly aged. Shortly after they share one last excursion to see a meteor shower, Himmel dies of old age. At his funeral, Frieren is overcome with a profound sense of regret, realizing that she never made an effort to truly know Himmel during their decade together, a period she had perceived as insignificant due to her long life. This guilt and sorrow become her main motivation, prompting her to embark on a new journey. Her goal is to travel to the far northern region of Ende, where it is said the souls of the dead reside, in the hope of meeting Himmel again to properly bid him farewell and express her feelings.

In this new journey, Frieren takes on the role of a mentor. At the request of her former comrade, the priest Heiter, she takes in a young, orphaned human mage named Fern as her apprentice. While Frieren is an incredibly powerful mage, her social clumsiness and the vast gap in their lifespans initially make their relationship somewhat awkward. Fern quickly matures, and their dynamic evolves; Fern often scolds Frieren for her childish habits and lack of practicality, effectively becoming the more responsible figure in their partnership. Frieren also later accepts the young warrior Stark into her group on behalf of another former party member, the dwarf Eisen. Stark serves as the party's front-line fighter, a role for which Frieren and Fern, as magicians, are unsuited. Frieren shows a quiet confidence in Stark's abilities, often teasing him or appearing unconcerned because she knows he is capable. Her relationships with her former party members, particularly Himmel and Heiter, continue to shape her actions through memories and flashbacks, as she reflects on the lessons they taught her.

Throughout the narrative, Frieren undergoes significant character development. She transitions from an individual who passively let relationships slip by to one who actively seeks to understand and connect with humanity. Her journey is not just a physical one to a distant land, but an emotional one to comprehend the value of the short, ephemeral lives of the people around her. She learns to take pride in her pupils, to express genuine care, and to honor the past not with distant nostalgia, but by applying the kindness and wisdom Himmel exemplified to her present interactions.

As a mage, Frieren possesses a vast arsenal of notable abilities developed over her thousand-year life. She is considered one of the most powerful mages in existence. Her signature technique is a unique form of mana suppression, where she constantly restricts her magical energy output to a fraction of its true total. She has maintained this suppression for her entire life, making it nearly impossible for others, especially demons, to perceive her real power. This allows her to consistently deceive opponents into underestimating her. When she fully releases her mana, its sheer volume is overwhelming, described as being as vast as a house or as turbulent as a storm. She was instrumental in the分析和 development of the standard offensive magic known as Zoltraak, originally a deadly demon spell that she helped adapt for human use. Her magical expertise includes powerful defensive magic capable of nullifying attacks, sealing magic that can immobilize targets for decades, and flight magic that she was among the first humans to utilize. Beyond combat, Frieren has a notable fondness for collecting a wide variety of mostly trivial or utility spells, such as magic to produce hot tea or clean rust from bronze statues, a hobby she has pursued since her days with Himmel's party.