Everyone Tames Beasts: I End Up Taming Diseases

Adrian is reincarnated into a world where everyone is a Beast Tamer. This is a world where the strongest rule. Everyone can form contracts with spiritual beasts to obtain great power.
One forms a contract with a gigantic fire dragon, while another forms a contract with a gigantic monstrous ape. A person even forms a contract with the legendary World Serpent—Jörmungandr.
Adrian forms a contract with diseases.
Hence, the gigantic fire dragon has the terrible flu and can’t stop sneezing. It sneezes fire everywhere and successfully burns its master to death.
The gigantic monstrous ape has terrible diarrhea. It exhausts itself from diarrhea and runs out of energy.
Meanwhile, the World Serpent Jörmungandr falls into a comatose state and isn't awake to fight for its master.
Is this really a power of this world? Such was the lament of everyone who fought Adrian.
Many years later, when facing challenges from countless people, Adrian spreads his arms and says, “Are you ready to be ruled by the God of Disease?”