The Hero Party [Holy Sword] (Excalibur), led by the charismatic Shin-Elf Will Striker, receives a chilling oracle: a traitor exists within their ranks and will cause their collapse within five years. Despite the oracle's infallible record, Will publicly dismisses the prophecy, asserting his unwavering trust in his companions: the taciturn wolf-human Rolf Avenne, the energetic twins Al and Haru, the shy dog-human Chloe, and the elegant Venus. However, Owen, the newest member and narrator, internally reveals that he *is* the traitor, driven by a fierce desire for revenge and ultimate power, viewing the prophecy as an opportunity to further his goals.
Following a successful dungeon expedition, the party celebrates at their usual tavern, [Moonlight]. Owen, a 17-year-old A2-rank adventurer, observes the party dynamics, noting the veterans (Will, Rolf, Venus) discussing serious matters separately from the newcomers. Their celebration is interrupted by Nero, the arrogant S2-rank leader of the rival party [Ascalon], who boasts of his and his new recruit's rank advancements. Will calmly deflects Nero's provocations, maintaining his composure. Later, Owen helps a drunken Al back to their grand headquarters. He encounters Venus, who, while expressing disbelief in the traitor prophecy, subtly probes Owen, leaving him unsettled and wondering if she suspects his true nature.
The next day, Al, Haru, and Owen plan a dungeon trip. Will, concerned about their safety against high-level monsters, offers to join, but Rolf interjects, volunteering himself instead. Will and Rolf share a cryptic conversation about "gardening," which Owen realizes is a cover for a secret, serious task, further cementing his suspicion that the veterans are hiding crucial information from the newcomers. At the guild in Alexandria, Owen selects the "Demon of Despair" for their mission, a powerful monster Rolf explains reveals one's true self and weaknesses.
Concurrently, Will secretly meets Alexia, a Shin-Elf "living prophet" deeply devoted to him. She confirms the oracle's prophecy is absolutely true. Will, despite his public facade, reveals to Alexia that he has "known the traitor's identity for a long time" and intends to defy the prophecy to protect his cherished companions. Alexia, who enjoys seeing Will's troubled expressions, finds his resolve "charming."
Meanwhile, in the Eastern Underground Labyrinth, Al's naive attempt to befriend the Demon of Despair fails. The Demon, a powerful monster from the Demon World that feeds on despair and absorbs vitality, pierces Al's stomach, causing him to bleed and lose his will to fight. Haru rushes to her brother's aid. Rolf, observing Owen, prevents him from intervening, coldly stating it's not his turn. Owen, driven by ambition, engages the Demon, using his orichalcum longsword (Spata) and superior combat experience to defeat it, despite its speed and durability. As the Demon dissolves, Owen's right hand glows, and his rank increases to A1, a significant step towards his goal of becoming the "strongest" in Alexandria and achieving his revenge, all while his party remains oblivious to his true nature.
