Demon Boss in the Human World - Chapter 31

A surgeon accidentally got the blessings of a system, shocked the medical industry, and rejuvenated countless people.

- Description from Novelupdates

“Born of Dragons, yet cursed by the Abyss—a king of two dooms.”----Ryuk Knull was nothing—just another powerless human in a world ruled by Titans, Vampires, and Fallen Angels. Until the Knulls came and took the only family he had left.On the brink of death, he awakened the Draconic Pets Evolution System—a power that doesn’t just tame beasts but binds them to his very soul. With it, mere monsters become apex predators.And Ryuk? He is their master.But power alone is not enough.He is a fusion of the most hated and the most divine—A being that should not exist.The abyss whispers. The dragons call. And when he rises—none will be spared.This is the Tale of the Abyssbourne Draconis!

In this world, Planet Earth had undergone great changes and humanity is faced with extreme danger. Luckily, humans have something called the Heaven Dao software.

However, he did not know that he was not raising just a harmless pet, but a biological weapon secretly made by the government… a real monster.

As a former librarian, Rand felt that he had been living an ordinary life, the one that he had reclaimed unconsciously every single day.

Recently, he has been a little upset because the pet fish he accidently brought home to raised seems to have undergo some strange changes

Well, it turned into a merman.

- Description from Novelupdates