Kanta na Enquete desu - Hotaru’s Case

As long as the land is square, Yan Bicheng should divide the world into four parts.
The dark organization “Ruyimen” has abducted children for many years, trained them as assassin agents, and sent them to the families of various countries for use in order to collect a lot of secrets, and gradually extended their evil hands to the court.
Feng Xiaoya, the favored minister of the King of Yan, suffers from bone melting disease. She is unparalleled in her “sickness and beauty”. For some reason, she abandons the eleventh wife, Qiu Jiang, and puts her under house arrest in the mountains. Qiu Jiang, who has forgotten his past, fled alone on a stormy night. After several twists and turns, on the way back, he met Yi Fei, the third prince of Cheng who was in trouble in a foreign land.
One wants to regain memory, the other wants to regain the throne. The two people who are incompatible with each other walk side by side towards Cheng in a bloody storm… but they find that the Ruyi Gate, which has been entrenched in Chengjing for a hundred years like a poisonous snake, seems to have undergone an unknown shock… …
The situation of the Four Kingdoms is back, and there is only one goal – to eradicate the evil organization Ruyimen!
However, as Qiu Jiang’s memory slowly recovered, a unparalleled secret finally surfaced…
Mrs. Ruyi, who is it? There is another mystery behind Ji Ying’s death?
What is the purpose of this return journey after a narrow escape, and where does it go?

- Description from novelbuddy

She is a top-class spy, a poison specialist, but also a young and cute girl with a sinister temperament. In spite of her sweet and innocent appearance, she can complete any tasks without the slightest hesitation. One day because of an incomplete black magic, she was sent into the body of a girl who was deemed as a good-for-nothing. What kind of change will she bring to this continent?

A Prince said with bitter hatred, “I thought she was weak and easily bullied, therefore I broke off the engagement. I really didn’t expect she is such a shrewd girl. I made an error of judgment.”

The Crown Prince deeply sighed, “She is such a sexy evildoer! Obviously, she has a frail and tender body, but I am not able to overwhelm her…”

Finally, an Emperor hit the nail on the head, “She is just a bit two-faced!”

She answered, “You’re just a big pervert!”

The Emperor carried her into the room and said, “You are predestined to be mine! A two-faced girl and a pervert are a perfect match, right?!”

- Description from Novelupdates

I was reincarnated into the world of a novel I’d only read the free chapters.

Thankfully, the blood flowing in the body of the person I’d possessed was blue.

“The prominence of our family comes from the blessing bestowed upon us by the royal family throughout the generations.”

Maybe this is the price to pay for that. But I got a father who seems overly loyal to the Emperor. And because of that, I was forced to become a Civil Servant.

While everyone else enjoys romance, I’m just spending my days as a Civil Servant.

She became the young mistress of the most powerful family in City T by marrying the young master in place of her sister.

He was cold to her on their first nuptial night. "Just because you played some tricks to get yourself married here, you still mean nothing to me!"

However, she was calm and heartless. "Young Master Mu, don't think too highly of yourself. I despise all that is you — your money and your very being!"

After the wedding, Young Master Mu lived lavishly by spending money like flowing during the day while working his nights away busily. "You said you despised me earlier. Well, which part of me do you despise exactly, hmm?"

Luo Chenxi could not bear the harassment any longer so she tossed out the divorce papers in rage. "I can't live like this much longer..."