Bell Cranel embarks on an eventful day in Orario, where he explores the Dungeon accompanied by Liliruca Arde and Welf Crozzo. The trio soon participates in the Holy Moon Festival, alongside Bell's goddess, Hestia. During the festivities, they witness Hermes presenting a challenge that involves extracting a spear from a crystal. The reward for the triumphant challenger is a blessing from the goddess of purity, entitling them to a journey outside the city. Encouraged by Hestia, Bell accepts the challenge. Upon his touch, he hears a voice affirming his selection, leading to the crystal shattering. Hermes praises Bell and introduces the event’s sponsor, Artemis, an old friend of Hestia's, who is taken aback to see her embracing Bell, referring to him affectionately as her "Orion."
Hermes enlightens Hestia's group about Artemis’ motive for sponsoring the event: she requires assistance to confront a menacing monster outside Orario that has been troubling her Familia. Although Bell doubts his capabilities compared to seasoned adventurers, Artemis insists that the spear's choice signifies his pure heart. Hestia supports taking on the quest, with Lili and Welf willingly agreeing to join in on the adventure.
After a week's journey riding dragons, the team reaches their destination and promptly saves a mother and her child from a horde of monsters. Bell demonstrates his skill by effortlessly defeating them using the spear. However, Hermes advises against using its power repeatedly. As the group sets up camp for the night, they discuss the recent outbreaks of monsters revealed by the mother. Hermes speculates that their current mission might be linked to these events. He recounts legends of a sealed monster named "Antares" from the Elsus Ruin, which has recently begun to regain its strength. He mentions that he and Artemis allied to defeat it, emphasizing the spear’s pivotal role in this endeavor. Hestia and Artemis find themselves deep in conversation about their feelings for Bell, with Artemis cryptically referencing past events with her Familia, while Hestia notes the significant changes she has undergone.
The next morning brings danger as the team nears their goal only to be ambushed by a barrage of light spears that force them to crash land into a desolate forest. Surrounded by a swarm of monsters, they are saved by Ryuu Lyon, who is part of Hermes' Familia, waiting for his return. Asfi explains the dire situation: monsters have ravaged the vicinity, blocking their path to Antares.
That night, as a comic relief, Hermes and the boys attempt to eavesdrop on the women during their bath, failing miserably. Amidst the chaos, Bell finds himself alone with Artemis, leading to an intimate conversation about their relationships and what Bell aspires to achieve. Their interaction culminates in a tender dance, where Artemis reminisces about the promise of romantic experiences the gods expected when they descended to Earth many thousands of years ago.
With a plan forming for their impending battle, the group strategizes, assigning Hermes' Familia as decoys while Artemis, Hermes, Bell, and the others launch their offensive into the ruins. They successfully navigate through the gate, courtesy of Artemis, but quickly find themselves overwhelmed by monsters that exhibit self-regenerative capabilities. Meanwhile, back in Orario, chaos ensues as dungeon creatures begin to act out violently, prompting the Guild to summon first-class adventurers to restore order.
Finally, Artemis’ group confronts Antares only to discover that its core contains the crystallized body of Artemis herself. Hermes uncovers that the Artemis traveling with them was merely a fragment of her original self. Having absorbed the fragment, Antares gains her divine power and unleashes catastrophic attacks, igniting what appears to be a second moon – a manifestation of an Arcanum spell known as "Artemis' Arrow." The Loki Familia and the Freya Familia galvanize efforts to fend off the irate monsters threatening to break free from the confines of the Dungeon.
Hermes further reveals the spear to be an arrow named "Orion," crafted by Artemis and capable of slaying gods. Asfi realizes the gravity of Bell's task: he is required to defeat Artemis. Bell rises to the challenge against Antares using only his Hestia Knife and Firebolt, but the formidable beast’s regenerative abilities prove daunting. Just then, the fragment of Artemis intervenes, thwarting an attack in an act of sacrifice before disappearing. Stricken with despair, Bell finds his resolve after hearing Hestia's anguished cries to save Artemis. Harnessing the power of Orion combined with his Argonaut skill, Bell slays Antares and utilizes his Hestia Knife to break the crystal encasing Artemis, ultimately piercing her heart.
An apparition of Artemis manifests before Bell, revealing that even gods have the capacity to reincarnate, though the timing remains uncertain. She expresses her hope that their next encounter will yield the long-awaited romance foretold by the gods. In the physical realm, as Antares disintegrates, the Arcanum spell dissipates, restoring peace to the monsters wreaking havoc in Orario. Outside the ruins, a somber yet relieved Bell finds consolation in Hestia's words, acknowledging that his courageous act not only saved Artemis but also rejuvenated the surrounding forest. Together with Hestia, they regroup with their companions and prepare to return home, richer in experience and friendship.
