The story begins with Shusaku Tanaka, a young boy burdened by a past life and a strict religious upbringing. In his previous life, Shusaku was a devout follower of a god, but his parents' fanaticism isolated him, leading to a lack of friends and a deep-seated anxiety about not being needed. He died from an incurable illness, only to be reborn as Seraph Engail.
Seraph's rebirth is marked by a dramatic scene where his mother, a former slave, presents him to a noble couple and a priest. It's revealed that Seraph possesses the rare "Enchantment Magic," a power that allows him to enhance himself and others. However, his father, a noble, dismisses him as "trash" for lacking the more common elemental magic, and Seraph and his mother are banished. They find refuge in the rural village of Nuunan, where they live a modest life working at the "Black Pig Inn."
Ten years later, Seraph, now a capable young boy, helps his mother run the inn. He's tasked with fetching ale from a nearby monastery. During this errand, he encounters Abigail, the innkeeper's daughter, and David, the innkeeper himself. They are concerned about Lyra, their cow, who has gone missing, a common occurrence in the village recently. Seraph, possessing the ability to use Enchantment Magic to enhance his physical capabilities, readily agrees to help search for Lyra after his errand.
At the monastery, Seraph reflects on his past faith and the nature of his current powers, questioning if his abilities are a gift from his former god or the world's goddess. He uses his magic to enhance his senses and tracks Lyra, discovering she, along with other livestock, has been abducted by goblins. Following them into the "Forest of Demonic Beasts," Seraph witnesses a horrific scene: Lyra is being devoured by hobgoblins. Overwhelmed by grief and rage, Seraph unleashes his combat abilities for the first time, effortlessly defeating the hobgoblins.
Injured and distraught, Seraph attempts to heal Lyra using his Enchantment Magic, but she is too weak. In a desperate act, he cuts off his own arm to provide his blood, rich with his magic, to Lyra. This act, combined with his magic, causes Lyra to undergo a drastic transformation, becoming a human girl. She reveals herself to be Lyra, who was saved by Seraph.
Their return to the inn causes a stir. Seraph's mother, Marie, is initially furious about his unauthorized trip to the Forest of Demonic Beasts, especially after discovering Lyra in human form. However, she eventually forgives him, understanding his desire to save Lyra. The inn's patrons, including David and his wife Laura, are astonished by Lyra's transformation. Lyra, now a human, integrates into the inn's life, becoming a beloved figure.
Meanwhile, Seraph continues to experiment with his Enchantment Magic, successfully brewing soy sauce. He also faces a misunderstanding with Abigail, who believes he was referring to her when he mentioned someone having an "accident." The story concludes with Seraph having successfully integrated Lyra into their lives, though the implications of her transformation and the presence of powerful monsters in the nearby forest hint at future challenges. The final scene shows a Manticore consuming Seraph's severed arm, hinting at a larger, more dangerous world beyond the village.
