Four centuries after saving the kingdom as the revered "Saintess" and then mysteriously disappearing, the immortal witch Astrea lives a solitary life deep within a forest, avoiding human contact. Her peace is disrupted when, caught in a heavy rain, she stumbles upon a crashed carriage and a severely injured young man. Despite her deep-seated desire for isolation, Astrea's compassion compels her to use her powerful, vitality-draining healing magic to save him and his horse, Razul. Exhausted and annoyed by the unexpected intrusion, she brings the unconscious man back to her rustic cabin, awkwardly tending to his wounds and struggling with the unfamiliar social norms of having a man in her home.
Upon awakening, the young man, Ios, is grateful but puzzled by his miraculous recovery. Astrea, trying to maintain her anonymity, dismisses his questions and rudely orders him to leave. However, Ios, a soldier stationed at a nearby fortress city, is persistent and returns days later to express his gratitude with gifts of food. Astrea, who no longer needs to eat for survival, initially rejects them, but the delicious aroma of Ios's homemade bean soup triggers an unexpected hunger, breaking through her centuries of detachment. Embarrassed but unable to resist, she eats, finding a forgotten pleasure in food.
Ios continues his visits every holiday, bringing different meals and even building a small outdoor stove at Astrea's cabin, gradually chipping away at her resolve to remain isolated. Astrea, though outwardly annoyed, finds herself anticipating his visits and the delicious food. She rationalizes that he'll eventually get bored or be transferred. This fragile routine is broken when Ios misses a visit. Astrea, despite telling herself she doesn't care, feels a pang of longing and decides to return an amulet he left behind, using it as an excuse to visit his city.
Upon arriving, Astrea discovers the city is in danger. A powerful monster, a chimera, has appeared for the first time in decades, and the military is struggling. Ios, now revealed as Vice-Captain Ios Forlight, is dedicated to protecting his people. Witnessing the threat and learning that the fort's only magic user is injured, Astrea's sense of responsibility overrides her desire for solitude. She confronts Ios, declaring her identity as a powerful witch and offering her aid, seeing it as "paying interest" on his kindness.
Ios's captain, Sfare, tests Astrea's abilities, but impressed by her skill and Ios's trust, he agrees to her cooperation. Astrea, riding with Ios to the combat zone, reveals her deep knowledge of chimeras, including their poisonous fire, tough hide, and vulnerable neck. She proposes a strategy involving a decoy, intending to take on that dangerous role herself due to her immortality. Just as they finalize their plans, Astrea senses injured soldiers and the chimera nearby, prompting Ios to rush towards the immediate danger with her, marking Astrea's full re-engagement with the world she once saved.
