The story begins with the protagonist, an 18-year-old male high school student from a rural background who was raised in an orphanage, on his way to a job interview. He is suddenly pushed onto train tracks by a stranger who shouts about the "resentment of Lady XX." The protagonist dies, only to awaken in a strange, ethereal space.
He is confronted by a cold, feminine voice accusing him of numerous sins involving women, theft, and playing with lives. Despite his protests of innocence and mistaken identity, he is subjected to immense pressure and then sentenced to be reborn in another world as a female succubus. His trial is to have relations with one thousand men, with a temporary thousand-year lifespan to achieve this. Failure means an eternity of suffering as a bug. He protests vehemently, but his pleas are ignored, and he is whisked away.
He awakens naked in a deep, verdant forest, disoriented and unable to recall his full name or the orphanage's name, indicating a memory restriction. He discovers his new body is female, with long black hair and a delicate physique. Overwhelmed and heartbroken by his unjust fate, he weeps before falling asleep.
He is awakened by the chilling presence of a wolf pack. Initially paralyzed by fear, he calms himself and realizes his new body possesses enhanced senses. He strategically retreats into a denser part of the forest, grabbing a sharp branch. When the pack leader attacks, he impales it through the mouth, killing it. The remaining wolves scatter. Though severely wounded, he survives, attributing his success to childhood experiences.
He washes his bloodied body in a river and finds shelter in a tree hollow. The next morning, he discovers his wounds have healed, confirming his immortality. He learns to fashion a rudimentary cup from a large leaf to drink water and uses leaves as toilet paper. He also learns to make tools and clothing from natural materials, surviving on wild plants and later, by successfully starting a fire and cooking fish and other small creatures. He also learns to defend himself, eventually defeating a pack of wolves with a stone spear.
His survival skills are tested when he encounters a large bear. Remembering advice from a past part-time job, he attempts to stand his ground and slowly retreat. However, a sudden distraction causes the bear to flee, and he, in his terror, wets himself. He returns to his shelter, reflecting on his near-death experience and the need for better defenses before venturing out to find civilization.
Meanwhile, at a border fort, Captain Dick and his subordinate, Uraki, observe a week-long, consistent smoke signal emanating from the protected forest. They speculate it might be a stranded individual rather than a poacher. The fort is responsible for protecting a mining town and the surrounding forest, which is rich in resources but has low magical activity and few demon beasts. However, the region has recently been infiltrated by boar-like demon beasts, posing a threat to the town. The fort is understaffed and faces bureaucratic hurdles in collaborating with local hunters. Despite the protagonist's likely male origin, Uraki humorously hopes the person in need of rescue is a "cute girl." Captain Dick, prioritizing life, orders a reconnaissance mission to investigate the smoke signal, preparing for potential encounters with demon beasts.
