Ghost Master: I Contracted Billion S-Rank Spirits

In a world overrun by fierce ghosts, over half the cities have been captured, shrinking the realm where humans can survive. Ghost masters have become the vital force protecting humanity and maintaining peace. Lin Mo accidentally transmigrated into a useless ghost master whose contract limit is merely 0.5. He accepts the system's ultimate mission to become the strongest ghost master and save all humanity, while also binding the 'Break Defense System' to unlock an overpowered skill that infinitely raises his contract limit with spirits.