One Piece: Fist of the World - Chapter 16: Sarquiss’s Efforts

Follow Chen Ming as he accepts disciples, establishes a sect, and fights his way in a world that deems him a cannon fodder.
He goes against any common sense using his wits and novel knowhow to finish missions and arm himself against his cruel fate.

- Description from Novelupdates

What is a young teacher to do when stuck with four cute little students in a beast apocalypse?. It's obvious, raise himself four little wives!!Well it's not his fault after all. They are the ones initiating it. As far as he's concerned, he's the victim of the story.“These four little devils, they are definitely after my back!”

He said coolly: “One million a month, stay with me!” She raised her eyebrows and smiled: “Pay a 30% deposit first, no credit!” Show no mercy. When the contract expired, she turned around gracefully, and when he chased after her, she found that there was already a kid the size of a kid beside her…

- Description from novelbuddy

A man is reborn into the world of Avatar: The Last Air Bender as a waterbender from Katara's tribe. Best of all, he was the same age as her, and he had a system with him to help.He knows the future and a system that lets him continuously get stronger by completing quests or long-term missions, as well as giving him the ability to copy abilities from others for himself. He will become invincible in the world of Avatar, even more so than the Avatar himself.