The System Mistook Me for a Cat - Chapter 5: Curriculum

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

Ukei Kaito fought a desperate struggle in order to fulfill his role as a summoned hero. He defeated the Demon Lord and saved the very world, only to meet an end filled but with betrayal. The companions that he’d trusted throughout his journey betrayed him and killed him by sticking a blade through his chest.

Luke is a half-beast who grew up in the twisty streets of a large city called Oukiwa. Abandoned by his parents as a child, he soon had to learn the arts of thievery to survive.

Even on the fringes of a super-powered society, he has followed a single rule all his life: never get involved with the Adventurers.

However, this rule is broken when his gang begins to hatch a plan to rob the most powerful family in town.

And so begins the chronicles of Luke Lange, a thief with no ancestors who in the future becomes one of the strongest men in history, with powers that are rivaling even the gods.

[WARNING: MATURE CONTENT 18+. Contains Netori, No rape. No Yuri]