A high-school class dies in a sudden classroom explosion and is reincarnated into a fantasy world, and one girl comes back not as a person but as a weak spider monster in the Great Elroe Labyrinth, the deadliest dungeon known. Trapped at the bottom of the food chain among frogs, snakes and worse, she survives on cunning and on devouring whatever she kills, leveling and evolving as she goes. Her classmates are reborn elsewhere as humans and elves, among them Shun, who wakes up a prince.