The story begins in the bustling adventurer town of Boltana, where the protagonist, Arc, and his childhood friend, Lynn, visit the Adventurer's Guild to register as adventurers and have their abilities appraised. Adventurers are individuals registered with the Adventurer's Guild who undertake various quests for rewards, ranging from monster subjugation to treasure hunting. Arc and Lynn, having grown up reading tales of heroes, vowed to form a party together upon reaching adulthood at sixteen. Arc harbors a secret desire to confess his feelings to Lynn once he has saved enough money as an adventurer, and to protect her.
When Lynn undergoes her ability appraisal, she is revealed to possess an exceptional "Hero Class" potential with a level cap of 80 and three top-tier priest skills: [Healing Magic], [High Priest], and [Goddess's Blessing]. This extraordinary result causes a stir in the guild, with everyone celebrating her miraculous talent. Arc, though surprised, encourages Lynn, expecting to have a complementary skill for their future adventures.
However, Arc's own appraisal yields a drastically different outcome. His level cap is a mere 1, meaning he cannot grow stronger regardless of his efforts, and his sole skill is [Instant Death Magic]. This skill is notoriously unreliable, with an extremely low success rate even against the weakest monsters like slimes, rendering it practically useless. The guild erupts in laughter at Arc's abysmal abilities, leaving him devastated and questioning his ability to become an adventurer.
Amidst his despair, a tall man in shining white armor, Allen, an S-rank adventurer and leader of a renowned party, approaches Lynn. He is impressed by her abilities and immediately invites her to join his party. The other adventurers are astonished, as Allen's party is known for its exceptionally powerful members. Lynn, despite her initial hesitation as a novice, is swayed by Allen's offer to help her grow and contribute to people's well-being. Arc's plea for her to stay is met with Lynn's tearful refusal, as she chooses to leave with Allen. Feeling insignificant and overlooked, Arc is left alone with his useless abilities.
Determined to pursue Lynn and retrieve her, Arc rushes out of the guild but is immediately confronted by a formidable, heavily armored man named Balzack, who dismisses him as "trash." Intimidated by Balzack's presence and the aura of his powerful party, Arc abandons his pursuit of Lynn, realizing he is not yet in a position to challenge such individuals.
Dejected, Arc heads to a nearby forest to test his [Instant Death Magic]. He attempts to cast it on a slime, but it fails, confirming the skill's poor reputation. Overwhelmed by regret and loneliness, Arc breaks down in tears. His despair is interrupted by the appearance of a Killing Bear, a B-rank monster. Despite his level 1 limitation, Arc, fueled by a surge of anger and a refusal to accept his fate, manages to defeat the Killing Bear with his [Instant Death Magic]. This victory triggers a system notification, revealing that his skill level has increased and he has gained skill points. He discovers that his [Instant Death Magic] has a limited effective range, explaining its failure against weaker monsters at a distance. He strategically allocates his points to improve the skill's range, success rate, and reduce its magic consumption, and gains the ability to store defeated monsters using [Coffin of the Dead] and convert their abilities using [Soul Collection].
Returning to Boltana, Arc sells the Killing Bear's materials to the guild for a substantial sum, earning 100 gold coins. He decides to prepare for dungeon exploration to further level up his skills, realizing the guild might become suspicious of his disproportionate strength. He purchases essential supplies and heads to a nearby dungeon.
Inside the dungeon's upper level, Arc encounters goblins and successfully defeats them using his enhanced [Instant Death Magic]. He gains stats and further improves his skills. He then faces a group of orcs, defeating them as well, and continues deeper into the dungeon. He discovers a beautiful, well-lit area with a safe zone where monsters do not enter. Here, he encounters a group of adventurers who are surprised by his lone presence and lack of equipment. He lies about his reason for being there and accepts their offer to return to town.
However, their path is blocked by a powerful Skeleton Ogre, a C-rank monster. Arc attempts to use [Instant Death Magic] but it fails, suggesting the monster has some resistance. He recalls Balzack's terrifying presence and realizes he must overcome such formidable foes. He repeatedly casts [Instant Death Magic], eventually defeating the Skeleton Ogre. This victory grants him a new ability, [Quadruple], which significantly boosts the range and success rate of his next [Instant Death Magic] spell at the cost of more magic. He also gains a substantial increase in his stats.
The adventurers he encountered are amazed by his feat and express their gratitude. Arc agrees to let them take the Skeleton Ogre's bones, asking them to keep his true abilities a secret. He returns to Boltana, intending to buy better equipment and continue his training. He rents a room at a discreet inn and plans to train at night to avoid attention.
The next day, Arc sells the orc meat and Skeleton Ogre bones to a shady shopkeeper for a meager 15 gold coins, realizing he cannot rely on the guild or such merchants. He receives a black cloak as a bonus. The shopkeeper reveals that the kingdom of Cretia relies heavily on adventurers due to a shortage of knights and soldiers to combat the increasing monster population.
That night, Arc ventures into the forest to train. He encounters a wolf-woman being chased by a shadowy monster. His [Instant Death Magic] fails against it, but using [Quadruple], he manages to drive it away. The wolf-woman, injured and unconscious, is brought back to town by Arc. They are unable to find lodging due to the town's popularity with adventurers and end up staying at the shopkeeper's establishment. Arc explains his adventurer status and his recent exploits to the shopkeeper, who offers him a clean room.
Meanwhile, Lynn, now level 15, is being trained by Allen, an S-rank adventurer. Allen's party is on a mission from the King of Cretia to find a "Key" hidden in the deepest parts of the dungeons, with the reward being a noble title and territory. Allen is concerned about other S-rank adventurers, like Balzack, also searching for the Key. He is patiently training Lynn, a rare healer with a high level cap, to aid in their exploration of the monster-dense dungeons. He believes that with Lynn's help, they can overcome the challenges and secure the Key before anyone else.
