MTL - Master of Ninja World - v16 Chapter 27 explain

An earthquake, another world, and a tentacle monster in his basement claiming to be his wife are just the beginning of a chaotic new life for Nick. He has new, dangerous, and exciting neighbors to get along with, people who want to kill him just for existing, and monsters with a taste for blood.But he's going to do his best to get to the bottom of everything and maybe even find a way back home. Even if he doesn't, he's at least not alone, for better or for worse.

Synopsis below:How did the Avatar universe change when a transmigrant appeared in an unknown village, long before the canonical events? And how are the two islands Kyoshi Island and Uzushiogakure no Sato (A village hidden in the maelstrom)?---Tags: AU, Before-canon, Post-canon, Violence, Death of major characters, Transmigration, Harem, Children, Incest, Romantic. Foul language.

He put one hand on the door beside her head before leaning forward. What was he doing? Trying to intimidate her again?

Chen Mu, a low-level officer, thought he could only live a cautious life, but unexpectedly he got a system panel that could accumulate experience, and he could master all the skills with just one practice.

[Blast Knife + Gale Knife + Wind Chasing Knife = Blast Artistic Concept]

[Jade skin grinding method + sand iron method + coarse salt method = skin of copper and steel]

A peerless martial saint with unparalleled swordsmanship, bronze skin and iron bones, and a body of pure gold was born step by step.

- Description from novelbuddy