Akame ga Kill: Starting with Dual Kamui - Chapter 13: Flirting with Other Girls

A good-for-nothing man married a beautiful girl but was kicked off the bed on the wedding night. Furiously, he wrote a bill of divorce and ran away.
He was schemed a car accident in which he nearly lost his life. However, it turned out to be a blessing. He swallowed the soul that passed through the outer world, thus obtained superb medical skills and martial arts.
Later on, with the silver needles and invincible martial arts, he embarked on the road of counterattacks and was committed to his great dreams.

- Description from Novelupdates

The protagonist, Punk, is a cautious, cold-blooded, and ruthless Mage.

His goal is always his top priority, over feelings or morality. When unnecessary, he doesn’t like to act like pigs to eat tigers; there are almost no life and death struggles, sometimes risky but steady progress. No strong enemy everywhere, Instead, Punk is always a strong enemy of others.

And he has a very keen interest in the secrets and teachings of the Netheril civilization.

The god king of Xiaoting in the upper realm fights down, and the spirit of the mixed dragon spirit is reincarnated on the earth, runs rampant in the city, and then fights in the sky.

Those who obey me prosper, those who oppose me perish!

- Description from novelbuddy

Zhang Xuan traverses into a foreign world and becomes an honorable teacher. A mysterious library appears in his mind. As long as it is something he has seen, regardless of whether it is a human or an object, a book on its weakness would be automatically compiled. Thus, he became formidable.

“Emperor Haotian, why don’t you like to wear underwear? To think that you’re still an emperor, can you pay more attention to your image?”

“Fairy Linglong, if you continue to suffer from insomnia, you can always look for me. I have a way with lullabies!”

“You as well, Qiankun Demon Lord, can you cut down on the garlic? Do you want to stink me to death?”

…

This is an incredible story about the heritage between teacher and students, cultivating and guiding the world’s strongest experts.