The story begins with the protagonist, Last, a twelve-year-old boy, waking up on the day of the "Blessing Ceremony." This ceremony marks their official adulthood and the bestowal of a "Sacred Artifact" from the gods, a weapon essential for fighting demons and monsters. Last dreams of becoming an "Adventurer," a protector of the people. His childhood friend, Ruby Blood, a spirited and outgoing girl, playfully urges him to hurry to the temple, reminding him of their shared dream to become Adventurers. Last, however, is nervous about the unpredictable nature of the Sacred Artifact he might receive, fearing it could hinder their dream. Ruby, though also anxious about receiving a suitable artifact, reassures him of their promise to become Adventurers together.
They arrive at the grand temple, which is hosting the ceremony for people from various villages. Among the attendees are parents of the candidates and Adventurers, likely scouting for talented individuals. Ruby quickly reunites with friends, leaving Last to wait alone. He is then confronted by Helio, a boastful and bullying boy from their village, who mocks Last's perceived weakness and the futility of his participation. Ruby intervenes, as she often does, defending Last from Helio's taunts.
The Blessing Ceremony commences. The first candidate receives a C-rank "Steel Great Axe," followed by a girl who receives a C-rank "Gale Dagger." The villagers are pleased with the high number of C-rank artifacts, as they are considered rare. Helio then receives a B-rank "Thunderclap Spear," earning him immediate admiration and recruitment offers from established Adventurers. Ruby, determined not to be outdone, steps forward and receives an A-rank "Flame Dragon Greatsword," astonishing everyone and attracting similar attention from Adventurers, including the legendary Hero Partia Lightning. Partia offers Ruby a place in her party, a prestigious opportunity.
When it is Last's turn, he prays for the strength to fight alongside Ruby and become a hero. However, the artifact that appears is a rusted, F-rank "Rusted Sword" with minimal stats. The crowd, including Helio, erupts in laughter, and Last flees in shame. He runs into the forest, where he is found by Hero Partia. She tells him he lacks the potential to be an Adventurer and advises him to give up, as he would only become prey to monsters.
Despite this crushing blow, Last is determined to prove them wrong. He begins training in the "Whispering Forest," hunting weak monsters called "Treants" with his Rusted Sword. His mother supports his decision, allowing him to focus on training rather than finding work. After three years of relentless, albeit difficult, training, Last's Rusted Sword has only slightly improved, reaching level 9 with a modest attack power increase. He learns that Ruby has become a "Platinum" class Adventurer, the second highest rank, and is known as the "Flame Swordswoman," serving as Hero Partia's right-hand.
One day, while training, Last encounters a "Demon," a sentient, higher-class demon with a black greatsword. The demon, seeking strong opponents, easily defeats Last. However, in a desperate moment, Last's Rusted Sword undergoes a transformation, evolving into an S-rank "Cursed Demon Sword" with immense power. He defeats the demon, saving a young girl who had been cornered. The girl's gratitude and his mother's unwavering support give him the courage to pursue his dream. He learns that his Rusted Sword can absorb other demon artifacts, gaining their powers.
Last sets out to the town of Milkrund to take the Adventurer exam. On his way, the woodcutter brothers he previously encountered apologize for abandoning him and give him a sword sheath, which perfectly fits his Rusted Sword. He finally embarks on his journey, determined to become an Adventurer and eventually catch up to Ruby.
