Ichiban Ushiro no Daimaou - Volume 3, Prologue

I woke up in my sleep, and a strange door appeared in my home…Behind every door is a strange world.

In the nightmare world, Jiang Cheng added the news from the strong man to the fat man, and he almost cried when he heard the latter, “If you die here, the whole family will stand upside down and bleed?”

“Is such that.”

“Then I don’t think you are too scared?” The fat man widened his eyes.

Jiang Cheng turned his head and said in a very formal tone: “Because I am an orphan.”

- Description from novelbuddy

Lyle Walt is a young noble boy and heir looking forward to the day he can inherit his family’s territory. Except around when he was 10 year old, his parents started neglecting him more and more in favour of his little sister, Celes.
On his fifteenth birthday, he is challenged to a duel by his sister to see who will inherit the household and horribly loses, being cast out of his family. Afterwards, he gets treated by the family groundskeepers and receives the family heirloom Gem from him that Lyle’s grandfather had entrusted to him. From there, he begins an aimless journey with his childhood friend and former fiancée, Novem, and the Gem-turned-Jewel that houses the memories, personalities, and Skills of seven of his ancestors.

Kenji had become the Emperor’s right hand man which he always wanted to be. He thought that this position would help him to become one of the most popular and powerful figure in history, He did not know that the newly crowned Emperor considered him as a threat. Secrets were being prepared to deal with this ‘dangerous subject’ who had become too influential to be ignored.“Oh, Dearest brother, I have to congratulate you on your well-deserved hire! How great must it feel to receive a court audience and the special joy of having a sword under your head before the imperial family!” The emperor said warmly.'Oh dearest sister... Your congrats are out of place... you just made the situation worse...'

The chief female forensic investigator, Ran Yan was secretly killed by her assistant. Unexpectedly, she was reborn in the years of the Tang dynasty. After experiencing a narrow escape, she fled from Jiangnan to Chang’an. Although, Chang’an was at the beginning of its flourishing period under the Li family’s Tang dynasty, various princes were vying for the throne by using all kinds of strategies. This was the dark days of the imperial court, where one needed to walk on a tightrope as one’s life was as powerless as an ant. The Xiao family controlled a large amount of wealth so inevitably they also became involved in the conflicts.

After arriving in Chang’an, she discovered many suspicious incidents: the original owner had unexplainable amnesia but his family was indifferent. She once again saw the orchid shaped clay inkstone, a valuable object that her mother has given her in modern times. Hence, could it be that she can time travel back? In order to survive in the Tang dynasty, she displayed her strong spirit and willpower by learning medicine from a doctor, pretended that she benefited from being sick on how to cure diseases, suffered hardship in earning money, manufactured penicillin, cured syphilis, and used her autopsy skill and experience to solve each and every murder mysteries.

- Description from Novelupdates