The story begins twenty years after the appearance of game-like dungeons, which initially caused global chaos. Humanity adapted, and within a year, international treaties and national laws were established. People gained stats and skills, and the allure of wealth from magic stones led many to become adventurers. However, the high mortality rate eventually tempered this rush, though the number of adventurers remains substantial.
The protagonist, Amamiya Kaede, a level 78 adventurer, is shown hunting orcs in an E-rank dungeon. He possesses a unique skill, "Magic Arrow," which allows him to create magical arrows using mana. Despite its unique nature, the skill is limited: it requires MP, its power scales with his Spirit stat, and the arrows don't automatically track targets, making it functionally similar to a regular bow and arrow. This has led to him being labeled a "jack-of-all-trades, master of none," ostracized by peers, and unable to join parties, forcing him to solo in E-rank dungeons. His goal is to become stronger, and he decides to spend his accumulated Skill Points (SP) to level up "Magic Arrow."
Upon reaching level 10, "Magic Arrow" gains a new effect: the forced acquisition of the "Lock-On" skill. This skill makes ranged attacks hit their target automatically. Kaede tests this new skill, finding it incredibly useful for hitting moving targets and making combat more efficient. He then attempts to solo a D-rank monster, a High Orc, the boss of the E-rank dungeon. He successfully defeats it by using his unique strategy of luring the boss out of the boss room, allowing the boss to reset and then attacking it from outside the room. This allows him to gain significant experience, leveling up three times.
He continues to grind by repeatedly defeating the High Orc, eventually reaching level 84. He then researches F-rank dungeons, realizing his MP is insufficient for efficient farming. He decides to move to an F-rank dungeon, the "Marsh Dungeon," known for its unpopularity due to its environment and slime monsters. He uses his "Lock-On" skill to defeat the boss, a Mega Slime, efficiently by luring it out of the boss room and attacking from the outside. This strategy allows him to gain considerable experience, pushing his level to 112.
During this time, Kaede also acquires new skills and upgrades existing ones. He learns "Appraisal" to check monster HP, upgrades "Item Box" for more storage, and significantly increases his MP with "MP Increase." He also upgrades "Lock-On" to level 5. He discovers that "Lock-On" is a unique skill, and having two unique skills would be extremely dangerous if revealed, forcing him to keep it a secret.
Seeking higher experience gains, Kaede decides to tackle a D-rank dungeon, the "Demon Dog Dungeon," which is much larger and more complex than previous ones. He encounters Kobolds, D-rank monsters, and learns that even with "Lock-On," they can dodge initial attacks. However, his skill ensures subsequent shots hit, allowing him to defeat them. He then faces the dungeon's boss, a High Kobold, a C-rank monster. Using his strategy of luring the boss out of the room, he defeats it repeatedly, gaining significant levels and SP. He upgrades "Lock-On" to level 10, gaining the "Multi-Lock-On" ability, allowing him to target multiple enemies simultaneously. He also upgrades "MP Recovery Speed Increase" and "Magic Arrow" for increased attack power.
While grinding in the Demon Dog Dungeon, Kaede encounters a mutant monster, a white Kobold, which is significantly stronger than regular Kobolds and poses a serious threat. He also finds himself protecting two children, including the boy Takuya he met earlier, who have wandered into the dungeon. Despite his injuries and his bow breaking, Kaede fights the mutant Kobold to protect the children, demonstrating his determination and growing strength.
