This Japanese Monogatari Isn't Lame - Chapter 40. Beichuan Si

[Starting MAY 19th, I'll upload 3 chapters per day, or at least 2 if I'm busy IRL.][Ding! Resurrection of the Dead can be used on this target.][Ding! Extraction of the Dead can be used on this target.]…When he was surrounded by thousands of his enemies, Kai decided to comply by extracting his 'strongest skill' in order to cause chaos and drag more people to hell with him.However, when Kai extracted his skill, he awakened an unknown power that made him feel that he had complete control over everyone's life and death.A mysterious old man awakened from his slumber when he sensed Kai’s power and decided to help him, as this could be considered a fate.Nevertheless, everything came with a cost…[Ding! Re-Awakening the host’s class.][Ding! An error has been detected.][Ding! Finding a solution…][Ding! Congratulations to the host, you have awakened the Immortality Lord Class (???)]

Bai Aoxue, the best mercenary in the 21st century, is accidentally sent back to the Chengxi Dynasty in Great Continent due to an explosion in her mission, and trapped in the first daughter of Prime Minister. After her rebirth, she is set up by her father to marry the 5th prince Jun Yeyan who wears a mask all day long.
In the face of bloodthirsty enemies, discord between brothers, collusion among courtiers and invasion of enemy state, can Bai and Jun resolve the crises? What will happen to their political marriage? How will the fierce battle for the throne end?
With many twists and turns, the book brings you to experience palace revolution, love and hatred thousands of years ago.

- Description from Novelupdates

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

Solver Keter, one of the Five Lunatics of Lawless City, regresses to when he was the illegitimate son of a doomed archery family.“If I regressed and couldn’t even save my family, I might as well go kill myself.”For my family? No, for my freedom!