Moto Sekai Ichi'i no Sub-chara Ikusei Nikki - Chapter 29: Quarrel

As the heir apparent of the Ye family, Ye Xuan went through fire and water for his family, but Ye Lang, who had just awakened his Divine Soul, usurped his place. In order to keep his position, Ye Xuan challenged Ye Lang to a Life-death Duel. With the broken Dantian, would he win this fight? The black ring his mother left brought him a great opportunity: Realm Hell Tower, where he met a mysterious lady, who told him to look for nine Daoist Laws to enhance his strength and gave him the Spirit Heaven Sword. Could Ye Xuan find all the Daoist Laws and become a powerful swordsman?

- Description from Novelupdates

When he wakes up, Su Changkong has traveled to a world where troops are chaotic and demons are rampant, and his martial arts qualifications are mediocre, but Su Changkong found that as long as his [lifespan] increases, his talent and potential can be [infinitely] improved!

Wu Qin Xi: imitating tigers, deer, bears, apes, birds and other animals.

Turtle Breath True Dinggong: Imitation Qigong, like a thousand-year-old tortoise breathing, breathing, breathing and closing for a long time, prolonging life!

Celestial silkworm magic: nine transformations of the silkworm, breaking the cocoon into a butterfly, rejuvenating the old and rejuvenating, opening the door of life and death, every transformation is a rebirth!

Cultivation of health boxing, practice the Qi of longevity! There are many corpses on the road of longevity, and Su Changkong has embarked on a longevity martial arts where heaven and earth are destroyed but I am immortal!

- Description from novelbuddy

A man who was once called the world’s strongest agent ended up becoming a teacher after his retirement, to train a new generation of agents. After many years of training his disciples, he was killed at the age of 60 by a secret organization’s ruse and was reincarnated in another world with his memories intact. Though he was surprised by the existence of magic and the strange species in that world, he quickly adapted to his condition as a newborn and took advantage of it. He acquired special magic and gained a massive amount of strength thanks to his rigorous discipline, in order to reach his goal: Resume his career as a teacher which he left halfway through in his previous life. This is the story of a man, who, based on the memories and the experiences of his previous life, became a teacher who travels through the world with his students.