Toaru Majutsu no Index: New Testament - Volume 6, Chapter 6: Monster, Monster, Monster, Monster. All_Bad_Stars.

Merged into the body of External Disciple Chen Yu was the heart of a demonic god.The heart is the core of life, the most fragile vital organ. To Chen Yu, however, the heart was his greatest strength, granting him power and potential beyond demonic and divine beasts. Here on out, we follow him as he embarks on a mysterious and wonderful journey.

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

He had served in the strongest Special Forces, Heavenly Sword Special Force. As the commando of commandos, he created the Netherworld in the western underground world and became the formidable Oriental Yama. He said, “I’m Liu Feng. I’m adept at two things: killing and saving. If I want to cure someone, even ghost soldiers can’t take him away; if I want to kill someone, God can’t save him.” Now he was the bodyguard of Yang Shiwen, who was the daughter of the richest family in Donghai City and suffered from a rare disease. Could Liu Feng save Yang Shiwen’s life with his amazing art of healing? What would happen to his double life?

Kai is the hardest working warrior in his generation... and the unluckiest. In a world where most people receive magical skills, classes, or cultivation, Kai has nothing but his wits and his strength. His only choice will be to forge a new path against fate, no matter where it takes him.

Savage monsters pour endlessly from the wasteland, threatening the survival of civilization itself. They say that human strength isn't enough and only those gifted with destined powers have a chance of making a difference. Kai is hungry to fight in that war, to be someone who matters. That hunger will take him across a world stranger and more terrible than he could possibly have imagined.