A classroom of Japanese high school students is reincarnated into a fantasy world, each transformed into a different being. The protagonist, previously an ordinary student, awakens as a low-level spider monster in a dangerous dungeon. Struggling to survive in a hostile environment filled with stronger creatures, the spider utilizes intelligence, adaptability, and a unique system of skills and levels to grow stronger. Through perseverance and strategic thinking, the spider evolves into more powerful forms, gradually gaining abilities to navigate the dungeon's challenges.

The narrative alternates between the spider's perspective and the experiences of her former classmates, who are reincarnated as humans, elves, and other beings in the surface world. These classmates, including Shun, a prince, and Fei, a dragon, face their own struggles and conflicts in a politically charged environment. The spider's journey is marked by isolation and survival, while her classmates grapple with societal expectations, power dynamics, and the mysteries of their new world.

As the story progresses, the spider's actions and growth begin to intersect with the events unfolding above ground. The world's mechanics, including its system of skills, levels, and reincarnation, are gradually revealed, tying the spider's survival to larger, interconnected mysteries. Themes of identity, resilience, and the consequences of reincarnation are explored as the spider and her classmates uncover the truth about their new world and their roles within it. The series balances action, strategy, and character development, offering a multifaceted exploration of survival and adaptation in a fantastical setting.