The Runesmith - Chapter 548: Hard Wall To Crack.

A boy from 21st century Earth, met an accident and later was reborn in Naruto’s Ninja World.
He is born in Uchiha Family and becomes the useless brother of Itachi Uchiha and Sasuke Uchiha…. Let’s see how he changed the Naruto world.

- Description from Novelupdates

Cain was an ordinary boy who loved creative works, especially when it involved anime and games. Suddenly, he found himself in a strange space with an extraterrestrial creature, a cosmic horror called Bishop that he couldn’t explain in words besides scary.Given the authority of a King, he was tasked to create dungeons in the multiverse in order to change his future. He had been turned into the Dungeon Maker. The more known his dungeon was, the stronger he became!Rias: What are you? A Devil?Dante: Now, now. What are you? Wow, I drank too much. Look at her, a sexy devil.Zoro: Where am I? Is that a sea monster? Good, I will bring meat for Luffy.Helldiver: For Democracy!!!All worlds became connected due to the dungeon. However, don’t worry!Everything was under his control.

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.