MTL - Aztec Eternals - Chapter 7 Father

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

After the real daughter of the Jiang family fell sick, she became stupid and insisted on marrying the cold-blooded, cruel, and crippled Fu Jiu. Mother Jiang said, "So be it. She's a good-for-nothing anyway. I only asked her to marry in place of my sister." Father Jiang: "After you marry him, remember to ask 9th master to help your sister find a better marriage." The fake heiress said, "Sob, I feel so sorry for Sister, but… if you get beaten to death by the 9th master, the Fu family will compensate us a lot of money, right? I'm looking forward to it." Jiang Li sneered. She bid farewell to her hypocritical family and brought her shabby dowry to the Fu family. After having been reborn once, she knew very well that Fu Jiu was the only person who treated her well. Everyone was waiting for Jiang Li to be beaten to death. Finally, one day, she was photographed by reporters and posted online. "It's all your fault! You used so much force last night! The Jiang family is going to laugh at me again!" Fu Jiuxiao said, "With me around, no one will dare to laugh at you. Moreover, I will make them pay back tenfold for the pain that the Jiang family has caused you!"

Huang Dan’s pain nerve is innately different from the ordinary people. A little tore in his skin can cause him to sweat all over his body painfully to the point of him unable to make a word out.

Somehow, he began to cross world, following Mr. System to do the tasks…

In the first world, Huang Dan realizes what it means to die painfully and to live to die again.

TL’s summary:
MC suddenly transmigrated and is bind to a system, requiring him to solve mysteries. Born with a higher degree of pain sensitivity, he met different people in the different worlds and learns what kind of emotion smiling is.

- Description from Novelupdates

An orphaned boy with dreams of making it big through being a blacksmith is given a once in a lifetime chance to succeed when he's taken in by an odd pair - Eggor and Ella. While former teaches him the arts of craft, the latter teaches him the mysticism of cultivation, granting him two paths to tread in this life.