Toaru Majutsu no Index: New Testament - Volume 8, Chapter 4: Disaster in the Depths of Fertility. Goddess_of_Fertility.

Welcome to Freia. A continent where evil magi ruled. Until firearms came, that is. Now the people live free of those demons…

It was a time where demons roamed the earth and chaos reigned. The story took place in Luoyang, the legendary capital of the times. During the night, one could find people holding on to their food with dear lives as they faced off against stray dogs, people with weapons in hand vowing to fight against Fate to their very last breath. There was bloodshed everywhere as some died meaningless deaths, while the strong tyrannized the weak and the truth was frequently hidden. Some of the citizens had completely lost their mind, while some died on their travels. Most importantly, the words of a certain youth caused much panic in the human world. It was a time of little warmth as nights in the capital were frequently accompanied by gusts of wind and rain, and it would be covered with snow during winter. Such were the days…

- Description from Novelupdates

Uchiha Yu traveled through and came to the crisis-ridden Naruto world.

Looking at the scarlet writing wheel in the mirror, Uchiha Yu nodded with satisfaction: “Well, everything is going well so far… smooth hammer!”

Looking at the calendar on the wall, Uchiha Yu felt the malice from this world…

In order to save his life on the night of the genocide, and even take food from the tiger’s mouth, Uchiha Yu decided to train Pokémon hard from today!

Uchiha Yume, use illusion!

A trainer: “Referee, Yu’s dream demon is illegal, it uses illusions!”

Uchiha Yu: “Humph, you absolutely cannot escape this technique!”

Deidara: “Explosions are art!”

Uchiha: “My Pangyan monster’s art is better than yours!”

- Description from novelbuddy

Anyone who could construct a stable Spell Model could become a Wizard — that was the Wizards’ ultimate secret! Having been given a new life as the son of an aristocrat and armed with a super quantum computer from his past life, Spell Models came as easily as breathing to Merlin. With this overwhelmingly huge advantage, would Merlin become the greatest Grand Wizard of all time?

- Description from Novelupdates