One Piece: Unreal Adventure - Chapter 20: I Call Bullshit!

When Zhou Yi woke up, he realized that he had become the prison guard of the Heaven Dungeon.Although he was fortunate enough to find a Fruit of Eternal Life, he did not possess any powers to protect himself.In a world of cultivation where demons and monsters roamed freely, Zhou Yi decided to hide himself and train for thousands of years.Time passed by quickly.The child he had freed 100 years ago had become the founder of the Great Qian Empire.The teenager he had helped 1000 years ago had become the elder of a celestial sect.The pet he had kept 10000 years ago had become the Absolute Demon King of Foreign Lands.This is the story of a normal person who has eternal life, the story of how he watched countless events unfold and eventually becomes the Supreme Celestial of Eternal Life.

After transmigrating into a weak noble body, Marvin discovered that he was familiar with the world, this was the game he played in his previous life and… Damn! He only had six months before the Great Calamity!

15 years ago the world discovered magic as well as mythical beings (basically beings from various legends) in another dimension. Humankind learned to summon these dangerous mythical beings and use their power to great effect. Seven countries formed contracts with these “mythical beings” and gained their allegiance as a result. The mythical beings will choose their summoners on their 14th birthday and give them a stigma. Schools have been set up to train summoners and magical swordsman (basically bodyguards that give the summoners time to cast their spell) as a result.

15 years later after the finding of magic Kazuki Hayashizaki is chosen as a summoner and given a stigma to indicate that. This is surprising since males aren’t chosen as summoners due to their low amount of mana compared to females. As the first male to be a summoner Kazuki is under a lot of scrutiny by almost everyone.

To complicate matters his sister (who’s a magical swordsman) is against him going into summoner school to train there as a summoner. Because summoners and magical swordsman have a cat mouse thing going on where summoners look down on magical swordsman as inferior so his sister naturally is against him going there. She’ll stop him even if it means going to war.

Kazuki however is determined to thrive in summoner school and has already determined to give it his all. Even if he’s the lowest ranked student (ranked E) and his fellow students intend to demean him he’ll prove himself as the strongest summoner.

An ordinary sect cultivator, with the help of the immortal mansion, gradually grew up in the cruel world of immortality, and his mind and body transformed together.

Mortal flow, partial dark wind.

- Description from novelbuddy