Naruto System in One Piece - Chapter 55

As a transmigrator turned extraordinary creature of the human race, he found the world to be more colorful than he had imagined.To more easily access everything this new realm had to offer, he first needed a special resume. Then, he had to find the right place in a city perennially shrouded in fog to fill out an application, and the last and most critical step...— was to kill a chicken or catch a mouse.

Le Xia traveled to the Marvel world. He was born ordinary, but after encountering a dilapidated bronze box, his life was destined to be extraordinary.

“Put on the holy clothes and protect the love and justice on the earth!”

The moment he touched the box, these words were imprinted into his soul.

Whether it’s evil spirits in the dark, covets in the starry sky, or “gods” who regard all living beings as playthings, all evils that try to disturb the peace of this land will face the justice of the saints.

When the golden holy clothes reflected the dazzling starlight and the white cloak fluttered without wind, the legend of the Saint Seiya began to spread throughout the Marvel universe.

- Description from novelbuddy

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