Tuco, once a powerless orphan abused by his stepfather and neglected by his mother, lives a life of pain and low self-esteem. His days are filled with beatings and hunger, and he grows up with no confidence, constantly reminded of his weakness. On a school bus ride, Tuco witnesses the class bully, Shogo, tormenting a kind girl named Ayaka. Shogo snatches Ayaka’s book, mocking her for reading "girly" novels, while the other students either support Shogo or remain silent to avoid becoming targets themselves. Despite his own insecurities, Tuco finds the courage to stand up to Shogo, only to be dismissed and ridiculed.

Unexpectedly, the bus and its passengers are transported to a fantastical new world. They find themselves in front of a majestic goddess named Isseus, who explains their new roles as heroes summoned to defeat a resurrected Demon King threatening her kingdom. The goddess reveals that they have been brought here to save her realm, and while some students express anger and disbelief, Isseus insists they have hidden abilities waiting to be unlocked.

To prove this, Isseus summons a fearsome demon dog that attacks a prisoner, showcasing the reality of the threat they face. After a student named Ayaka demonstrates powerful abilities by incinerating the demon, Isseus tests each student's skills using a crystal ball. Some students reveal impressive A and S rank abilities, while Tuco's turn reveals a disheartening E rank, the lowest possible. This rank signifies a history of failure and troublemakers, and Tuco is cast aside with little hope of survival.

Isseus, determined to discard the weakest link, assigns Tuco to a dangerous dungeon where failed heroes are sent.

Tuco is given a useless leather bag and warned that if he fails to survive, his life is forfeit. The goddess and the others dismiss his pleas and arguments, showing no sympathy for his plight. As the dungeon ritual begins, Tuco is thrust into a dark cave, overwhelmed and terrified. He struggles with his low stats and the constant threat of death from powerful monsters.

In the cave, Tuco’s fear nearly overwhelms him. He is nearly killed by a monster but manages to use a paralysis spell in a desperate attempt to survive.

As he continues, he encounters another formidable demon and realizes his paralysis spell works effectively. Despite exhaustion and dwindling mana, Tuco uses his final spell, a poison spell, to defeat the demon.

This victory marks a turning point for Tuco. His success in overcoming the dungeon's challenges reveals his latent strength and determination. Although he starts as the weakest among the heroes, his struggle and resilience in the face of overwhelming odds begin to reshape his destiny.