The story begins with the protagonist, Lilialys, a 16-year-old Marquis's daughter, experiencing a near-death incident. Her carriage tumbles down a cliff, and as she lies injured and fading, she recalls her past life as a forty-year-old single woman from Japan. This past life memory, filled with a mundane existence but a passion for "oshi-katsu" (fan activities), clashes with her current life's harsh reality.
In this world, Lilialys was born a twin, initially doted upon by her parents due to her abundant magic. However, at age eight, her magic was revealed to be of the light attribute, considered useless and incapable of offensive spells. This led to a drastic change in her parents' attitude, resulting in her being relegated to a life of servitude in the attic, treated worse than a common servant. Her twin sister, Yumelia, possesses the rare and valuable holy attribute, destined to become a saint and engaged to the First Prince.
At sixteen, Lilialys is forced into an arranged marriage with Duke Alfred of Ashran, a man twice her age and exiled to a remote, dangerous, and impoverished territory. This marriage was arranged because no other noble families were willing to send their daughters to such a desolate region. Lilialys's past life memories, however, offer a glimmer of hope; being far from her manipulative family and the capital, and marrying a duke who is rarely present, means she can live a life free from their scrutiny and potentially pursue her "oshi-katsu" with fewer constraints.
Despite her newfound resolve to live, Lilialys is gravely injured. Her light magic, previously deemed useless, becomes her only means of survival. She uses it as a signal flare, attracting the attention of knights who find her. She awakens in Duke Alfred's manor, tended to by a kind maid named Martha. To her shock, she learns that during her three-day unconsciousness, she was married to Duke Alfred.
The narrative then delves into Lilialys's attempts to understand her new circumstances. She discovers that her light magic, while not offensive, can create light and that her past life knowledge might be useful. She begins experimenting with her magic, trying to understand its properties and limitations, comparing it to concepts like batteries and LEDs from her previous life. She also learns about the harsh realities of her new home, the Ashran territory, which is frequently attacked by monsters and has a difficult climate for agriculture.
Lilialys also receives a letter from Duke Alfred, written in a hurried and messy hand. The letter reveals that their marriage was an arrangement of royal decree and that he intends to have a "white marriage" for three years before divorcing her. This news, coupled with the realization that her carriage accident might have been orchestrated and the subsequent discovery of her family's disdain and her sister's perceived superiority, fuels Lilialys's determination. She resolves to make herself useful and find joy in her new life, even if it means living with a distant husband and facing the challenges of a monster-infested land. The chapters end with Lilialys embracing her new reality, finding a sense of purpose in understanding and utilizing her light magic, and looking forward to discovering new "oshi" in this magical world.
