There's No Love In the Deathzone (BL) - Chapter 373 - 365. House Trial

A man was transported to Ancient China and eventually became a servant of a declining household without a male heir. He utilized his wits and modern knowledge to help the household and eventually become trapped in the sea of political turmoils of the period.

- Description from Novelupdates

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.

A tale about the former leader of a special organization that served under royalty, now leaving his past life behind and unintentionally getting involved with the martial world.

Reincarnation's a rare gift, but Ning Qué's second chance comes with a twist. Betrayed and brutally murdered by his own mother, Oliver's fate takes a dramatic turn - rebirth as Ning Qué, an E-Rank hunter in 2027. Armed with a Player System cheat code, he's poised to defy destiny and rise through the ranks. But can he outsmart fate, or will his unluckiest streak haunt him forever?