Adolescent Adam - Volume 3, Chapter 4 - Fading Borderline

Born of a great family, world shaking genius.

A con-man and policewoman that are legends of their respective professions suddenly die, then are reincarnated and return to the Tang Dynasty of ancient China as little kids.

Accepting their second chance and forced restart, they choose to use the modern knowledge and specific talents that they have in their previous lives in order to live comfortably in this new life.

- Description from Novelupdates

I am serious about saving people, I am professional in protecting people, and I like hunting for treasures. . . .

Emergency doctor Lu Fei was forced to travel to a small town in the United States in a parallel universe, got the rescue system, and became a legal mercenary by chance.

As a real man, you must always cut open people’s bodies to save people from danger; you must often fight and kill, and use thunderbolt methods with compassion!

- Description from novelbuddy

Qin Tian accidentally transmigrated into a sickly body, a body with broken Dantian that was unable to practice Qigong, in another world. Fortunately, God had mercy on him by giving him a level up system. Useless? That was him in the past. Not worrying about practicing Qigong, he was now able to kill Monsters to level up. Easy! Level up when killing Monsters; level up when killing people. An unbeatable sovereign of the clan in the eyes of other people, but in his eyes, he is a glittering big BOSS.