One Piece: Unreal Adventure - Chapter 5: Teach Me Something Gramps!

Cheng Feng, an ordinary young man. He isn’t genius, however, his elder sister has a unique body, Nine Linglong Body.

One day, his brother in law awakes an eight order martial spirit and become a peerless genius in Hidden Dragon Academy. In another side, he can reach that step because of receiving the help of Cheng Feng’s elder sister.

When Cheng Clan’s people think that their clan will rise and advance to a higher status, but this is the beginning calamity of Cheng Clan. Their talented son in law writes off the marriage,

Cheng Clan Patriarch dies…

….

His elder sister commits suicide…

After Cheng Feng sees the calamity of Cheng Clan, his heart is wrath, he only wants to revenge to the people who cause his clan fall to this step.

” I will take revenge to the people who make…”

But he doesn’t have the strength to do it until he hears a mysterious voice…

- Description from Novelupdates

On the day I went to the hospital for an abortion, I met my husband holding his ex-girlfriend. That woman was just suffering from menstrual pain, but he was taking great care of her and being very gentle.He said, “I never thought of marrying you, so please behave yourself.”He said, “You are just a scheming and fickle woman. How could you bear my child?”I sneered and decided to abandon him!After the divorce, that woman showed off their engagement ring to me. Then, I pointed at the man who had just walked into the hotel and said, “Let me introduce. This is my new boyfriend.”Since then, this tycoon, who was only temporarily working as a doctor out of boredom, somehow got a girlfriend who had come to him for an abortion.

“You call yourself a hero? After your greed killed my sister?”What would you do if all of your friends, everyone you ever loved besides your sister, died in front of you?What would you do if, because you were weak, everyone hated you and considered you a Wasted, someone who hurt humanity's chance to survive extinction?Adam continued fighting despite this abuse, because he still had 1 simple goal: even if he was nothing more than cannon fodder or wasted potential, he would keep his sister safe.But then, it wasn't the Kaiju or apocalypse that killed her. It was the Exalted, the strong, the heroes of society.The people he was supposed to praise were the ones who took his last hope in life away before killing Adam as well.So, when he regressed with a villain system that rewarded him for killing Exalted...[First Exalted killed!][Artifact: The Mantle has upgraded to level 2!]

While the demons were rising, mankind was about to become extinct. Six temples rose and protected the last territory of mankind.

A young boy joins the temple as a knight to save his mother. During his journey full of miracles and tricks in the world where temples and demons are antagonistic to each other, will he be able to ascend to the strongest knight and inherit the sealed divine throne?

- Description from novelupdates