Filma is an E-rank adventurer who spends his time diving into dungeons to gather medicinal herbs. He is scorned by fellow adventurers, who mockingly call him the "Eternal Herb Picker." One day, Tina, an S-rank adventurer aiming to reach the dungeon's deepest level, finds herself in dire straits after encountering an anomalous monster. Just as she resigns herself to her fate, who should appear before her but... none other than Filma, the "Eternal Herb Picker"! Although Tina initially assumes the opponent is far too dangerous for an E-ranker, the "Plant Magic" Filma wields proves to be overwhelmingly, extraordinarily powerful!? Thus begins the epic tale of the "Eternal Herb Picker," the adventurer with the title of "Weakest" as he unleashes his unrivaled might!