MTL - Harry Potter and the Rise of the Ordinary Person - Chapter 43

Lu Zhou wakes up to become the world’s most powerful and oldest villainous Patriarch, and finds that he has nine notorious disciples who are full of evil. His eldest disciple is the leader of the Nether Sect with thousands of minions, and his second disciple—Sword Devil—always slaughters others at the slightest disagreement…

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

In a dark space secluded from the rest of the known galaxy, a young man wakes up in a struggle for his life.During his coming of age ritual, it was revealed that he possessed the heavy soul body, A talent that could potentially rival even the gods. Joy overtook his entire household as they prepared for the eventual rise of their clan.But on that same day, the Hand of judgement fell upon them extinguishing all traces of life on their planet leaving it as a dead world…As for him? Fate had other plans. Cast into the darkest and most secluded place in the known universe, The sanctuary, he is faced with a decision, become stronger and survive or wallow in misery and Die![You have Awakened ][ Hidden Class Unlocked : SSS Soul King— Supremacy over all Souls and soul kin ][ Innate Skill unlocked: Heavy soul brilliance— In the following 20 seconds host will become effectively Unkillable]-—WSA Entry-—

A modern-day antihero, who was infamous for his devious acts, dies in an explosion meant to take down a powerful criminal syndicate. Waking up in a world of sword and sorcery, he finds himself possessing a fragile, powerless body with a strange “System” that seems broken. Initially thinking he's doomed, he learns that by pretending to be weak, he can manipulate others into revealing their secrets, granting him abilities they possess. As he rises in power, he discovers that the System was intentionally sabotaged—by none other than his own future self.