In Different World with Naruto System (WN) - Chapter 09: Awakening Mangekyo Sharingan

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

“Brother Katakuri, I’m sorry, I don’t want to bear the name of Charlotte for a long time!”

“Ace, your flame is too weak!”

“Akainu, magma is dessert to fire dragons! Why don’t you understand this?”

The man who ate the dragon fruit, the traitor of the Charlotte family, sprinted towards the title of One Piece!

- Description from novelbuddy

A cauldron, a secret forging method, and his blood created an ultimate weapon. The youngest Sword Crafting Master on Earth had been reborn from another world. With the Nine Yang Divine Furnace and a scroll of Divine Equipment, he was like a fish in water, standing at the pinnacle of the martial way. There were tens of thousands of clans, billions of cities, and countless experts. He was the master of ups and downs!

God gave me one more chance and finally came back after four hundred years.

As soon as I realized I returned, I decided that ‘no one should have pride.’

My goal was to destroy the country. So, I grew up with a genius prince who lived in hiding before returning.
He took up the empire for me and I left him for him to achieve his goal.

‘I came to pick you up Charlize Ronan.’ Dylan, who became a perfect tyrant after a few years, found me after searching all over the continent.

‘Why did you flee and run away?’