The Legend of Sun Knight - Volume 7, The Seventh Chapter to Ending the Demon King: “The Demon King’s Choice”

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

Tian Long, an orphan without much of a life in both his thirty year long life and lifespan!
To him, a single opportunity was displayed to transmigrate into another world with his Death Book!
"What's this? Is this the body of a three year old? Davis? Is this my name from now on?"
Finding himself possessing a small child, he becomes inwardly conflicted before he faces the truth and his reality!
Young Davis finds himself as the legal heir, the Crown Prince of the Loret Empire in the Grand Sea Continent, becoming a powerful cultivator in a short time...
However, is that all?
Follow his journey as Young Davis becomes a full fledged death's advocate while embodying into the Divine Emperor of Death in the world of cultivation!
"Mn? The route to become the Emperor is a given? Nah, I still don't want it..."
"Oh? I'm courting death you say? Unfortunately for you, death is already my woman..."

【Nonsense】【No morals】【No routine】

…

The majestic world, nine heavens and ten earths.

In a colorful world, happy cultivating immortals.

When Chu Liang opened his eyes, he found that he had become a disciple of the Shushan School, and he was carrying a strange pagoda… Since then, he has embarked on an unimaginable road.

The thirty-sixth peak rises in the morning smoke, and the dragon is returned eight thousand miles away!

…

“My lord, please kill the demon!”

- Description from novelbuddy

The empire has turned into the land of the undead due to a spell gone wrong. God summoned heroes from countless worlds to purify the empire and plant new hope. Lee Shin Woo, an ordinary earthling, was also summoned. As an undead, that is.