Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 15 - 15-23. The Forbidden Science

Three years ago, the animals and plants on Earth underwent crazy and unexplainable changes that included transformations, reversions, and the addition of otherworldly species. And it was the start of a brand-new type of profession in the new generation of humanity – Monster Trainers, people who specialized in taming monsters.

On his 18th birthday, the protagonist of the story, Gao Peng, suddenly received the ability of being able to see the attribute data frame of monsters. With his ability, he aspired to become the strongest monster trainer that ever lived while looking for a method to revive his parents!

- Description from Novelupdates

How can there be any invincibility?

How can there be any Xeon undefeated?

No one in this world can be eternally number one, anyone can be defeated.

including me.

I’ve been waiting for that one person to show up, beat me, tell me that my way is wrong.

It’s a pity that that person hasn’t come yet.

…

False martial arts: strengthen yourself, break the limits of the human body, and resist bullets with flesh and blood.

Real martial arts: use the magnetic field of life to dominate the magnetic field of the stars, use the small universe of the human body to attract the power of the big universe, travel the starry sky, and smash the planet.

- Description from novelbuddy

Mason was a mercenary, until the day he died on a mission after being betrayed by his unit.

Humanity’s first 8th Class Mage.

Betrayed, he traveled back 30 years into the past.

The story follows Ian Page, archmage and the first man to break through the 6th class, then through the 7th and become the most powerful mage, an 8th class mage.

After a lifetime of war and killing, the continent was finally unified thanks to his efforts. Now, old, his wish is to live the rest of his life in peace and try to find salvation for all the blood he spilled. However, his old friend, maddened by paranoia, couldn’t tolerate someone so powerful, so he betrayed Ian and killed him.

In his last breath, he cast a time magic that allowed him to travel back to when he was a young boy. With all the knowledge he previously had, he decided to do things better so he could end with less regrets.