The story begins with Vino, an "Item User" and support member of the A-rank adventurer party "Assault," facing criticism from his teammates after a quest. Ostal, the tank, throws a bottle at him, while Rune, the sorceress, berates him for being useless and slow with item management and healing. Amina, the grappler, offers a token of encouragement, but even she likely harbors dissatisfaction. Tommy, the party leader and warrior, suggests they need a dedicated healer. Vino, having been with Assault since their D-rank days, feels like a burden as he hasn't kept pace with their rapid growth. Their goal is to reach S-rank, which brings national quests, immense rewards, and honor.
Vino's "Item User" class is considered the weakest and most bottom-tier, with few practitioners in recent years, and a past user's incompetence has tarnished its reputation. Despite his efforts in various support roles and even attempting sword and magic, Vino's talent lies solely in item manipulation. He acknowledges his limitations, especially with the party aiming for S-rank.
After the party leaves him to clean up their mess at their usual bar, Vino overhears other adventurers mocking him as an "orphan adventurer" and a "useless item dealer." He contemplates quitting adventuring altogether. His attention is then drawn to a striking woman entering the bar: Candia, an A-rank adventurer. Despite her beauty and skill, she is ostracized due to a local superstition associating black hair with death. This forces her to adventure alone, and she appears to be struggling, her armor showing signs of battle and her healing potions likely depleted.
Vino, despite his own struggles, offers Candia two of his potions. She is initially suspicious, but Vino drinks one to prove it's not poisoned, then presses the other into her hand. He leaves, planning for his upcoming S-rank trial, which he intends to skip by leaving the party after their next quest. Candia, after some hesitation, drinks the potion and is amazed as her wounds heal completely.
The narrative shifts to the party's next quest: defeating a Poison Cerberus in an ancient ruin. Rune unleashes powerful fire magic, while Ostal, Tommy, and Amina engage the beast. Vino provides MP-restoring Magic Potions to Rune and special, custom-made potions to the front-liners when they are injured by the Cerberus's poison breath. Despite their coordinated efforts and Vino's crucial support, the party defeats the monster. Tommy, surprisingly, thanks Vino, acknowledging his contributions and suggesting they can now attempt the S-rank trial. However, in a shocking betrayal, Tommy stabs Vino, and Rune burns his back. They reveal their plan to use the "Party Loss Compensation" system, which provides a payout and replacement member when a party member dies, to bring in a new healer and strengthen their party for S-rank. Ostal gleefully loots Vino's item bag, claiming the items he made himself. As Tommy prepares to deliver the final blow, a massive Tyrant Dragon descends, devouring the Cerberus. The party flees, leaving Vino to face the dragon alone.
Just as the dragon is about to attack Vino, Candia intervenes, skillfully fighting the S-rank monster. Vino, realizing she is risking her life for him, uses his last potions to heal himself and distract the dragon, allowing Candia to land a decisive blow with her greatsword, "Ichinokata: Ochiba," defeating the Tyrant Dragon.
Vino awakens to find himself on Candia's lap in a safe area within the dungeon. He learns that Candia carried him there and expresses his gratitude. He explains his betrayal by Assault, and Candia, in turn, is surprised by his abilities, particularly his powerful potions and his unexpected strength in throwing the potion bottle with such force that it embeds in a wall. They discuss his "Item User" class, which is rare and misunderstood, and Candia reveals that his custom potions are akin to legendary elixirs. Vino begins to realize his own potential, which his former party had dismissed.
They decide to part ways, with Vino heading to a craft town and Candia returning to the trading city. However, Vino asks Candia to form a party with him, admiring her strength and beauty, especially her black hair, which he finds captivating. Candia, deeply moved by his acceptance and compliment, mistakes his proposal for a marriage proposal and enthusiastically agrees to "marry" him the next day.
The next day, Vino and Candia, now a party, take on B and C-rank quests in a craft town. Vino's potent potions prove effective in combat, quickly dispatching wolves. Candia, initially disheartened by the negative comments about her black hair, is encouraged by Vino's unwavering support and belief in her. Vino, recognizing his own newfound combat abilities and Candia's need for support, resolves to train his potion-throwing skills and work together with her. Candia, still somewhat flustered by Vino's proposal, continues to act as his devoted partner, even preparing meals for him. They discuss their future plans, with Vino intending to support Candia in combat while he focuses on his item-based abilities.
