The protagonist, a lonely and envious college student, dies tragically on Christmas Eve while saving a high school girl from a speeding car. He awakens in a luxurious room, having been reincarnated as Grayve Undertaker, the villainous lord from an erotic game he played, "Busty Fantasy." Initially thrilled by the prospect of a harem and escaping his previous virgin life, he quickly learns that Grayve is a weak character with no special abilities, destined to be killed by the protagonist. However, he discovers a hidden, unawakened divine protection.
His first interaction is with a busty maid named Narvi, whom he treats with uncharacteristic kindness, aiming to increase her affection. This kindness, a stark contrast to Grayve's usual cruelty, surprises Narvi and begins to alter her perception of him. He also learns that Narvi is the personal maid of Dorothy, Grayve's adopted sister and a main heroine in the game, who is a powerful but sickly mage. Grayve's father, also a cruel figure, agrees to provide Grayve with a sword instructor, a former vice captain of the royal guard, after Grayve claims he wants to become stronger for a woman he admires.
Grayve begins training diligently, his swordsmanship improving rapidly. He continues to be kind to the busty maids, including Narvi, further raising their opinions of him. He encounters Dorothy, a beautiful but emotionless girl, and her cold demeanor and sharp observation skills make him wary, suspecting she might sense his true nature. He also overhears maids discussing Grayve's terrible reputation, making him question if Narvi's kindness is genuine or an act.
A quest to find a rare herb for Dorothy's medicine arises. Grayve sees this as an opportunity to gain favor with Narvi, recalling a "reward sex event" in the game. He volunteers to go, accompanied by Narvi and, unexpectedly, Dorothy, who insists on joining. During their journey, they encounter goblins, which Grayve swiftly defeats, showcasing his improved combat skills. He then prompts Dorothy to use a powerful ice magic to freeze the remaining goblins, a tactic that unexpectedly alleviates her symptoms, leading her and Narvi to believe he has discovered a cure. This event further boosts their affection and trust in him.
Their quest leads them to a cliff face where Dorothy struggles to climb due to her weak physique. Grayve, despite his internal reservations about Dorothy (a "flat-chested" heroine), carries her up the cliff to impress Narvi. He also learns that Dorothy has a trauma related to using magic on people. He uses his game knowledge to encourage her to unleash her full power against a powerful monster, an "Erol," that attacks Narvi. Dorothy's powerful magic, amplified by her own divine protection, defeats the Erol.
However, their victory is short-lived as a colossal "Mithril Turtle" awakens. Facing overwhelming odds, Grayve feels despair but is spurred by his desire to fulfill his dreams and protect the women. He awakens his own divine protection, "Hephaestus's Blessing," which grants him skills related to forging and fire resistance, but also a "Woman Trouble" debuff that weakens him around women and a "Lustful Desire" status that will cause him to lose all his powers if he loses his virginity. He uses his new abilities to fight the Mithril Turtle, buying time for Dorothy to prepare a powerful ice spell. He then instructs Dorothy to use her magic, even if it means hitting him, to defeat the monster.
After the battle, Grayve wakes up in bed, with Dorothy clinging to him and Narvi watching over him. Dorothy reveals she believes he is a savior from another world who has taken over Grayve's body, attributing his kindness and knowledge of her illness to this. She expresses her love and desire to help him achieve his dreams, misinterpreting his desire for a harem as a noble goal. Narvi also expresses her happiness at their improved relationship. Grayve realizes his "Lustful Desire" status is a double-edged sword, granting him power but risking its loss upon losing his virginity. He resolves to gain the affection of women before acting on his desires.
Later, during sword training, Grayve practices using his new skills, including creating a Mithril shield. He also learns about the "Athena Knights," an all-female, busty knight order, and plans to meet the sword instructor's daughter, a member of this order. Narvi continues to show him affection, and Dorothy, now more affectionate and less emotionless, joins him for meals, even sitting on his lap. The chapter ends with Grayve contemplating his next move to achieve his harem goals, while Dorothy, convinced he is her savior, dedicates herself to helping him.
