One fateful day, a mysterious place called the "Abyss," which is full of celestials and monsters, appeared on Earth. These celestials from the Abyss required the faith of believers to maintain their power, making Earth and its great population a jackpot for them. Unfortunately, among the good celestials who handed out blessings to humans in return for their faith, there were evil celestials who preferred to use more powerful means to just take over Earth. Yeonseung Choi is one of the many hunters on Earth who protect people from the threat of the dungeons and the monsters that come from the Abyss. However, he is obsessed with training and becoming stronger, to the point that a celestial has a vision of him saving Earth from a calamity involving demonic celestials swallowing up Earth whole. Thus, she makes a contract with him to have him train and become the hero from her vision. Will Yeonseung really be able to endure the arduous training in the Abyss and return to Earth to save it?