Hajime Nagumo finds himself in a fantasy world with classmates who constantly bully him. While everyone is revealed to possess cheat skills perfect for battle, Hajime only finds himself with a seemingly useless ability as a Synergist. Weakest even in another world, he ends up at the bottom of the Abyss due to a classmate's betrayal! With no way out, Hajime falls into the depths of despair... until his fateful encounter with the vampire Yue paves the way for him to become the strongest synergist. "I'll protect you, and you'll protect me. We'll be unstoppable... ...and surpass the entire world, together!" The "Strongest" Isekai Fantasy begins with the story of the boy in the abyss and the hidden vampire! —And thus the boy becomes the "Strongest".