This Japanese Monogatari Isn't Lame - Chapter 7 - . Dagger Jian Ding (Please Collect!!!!)

Scheming female assassin transmigrated to become the weak Eldest Miss, her story is wonderful and stunning, attracting peach flowers to blossom open. Cold calculating emperor? Genius bad crown prince? Insidious happy-go-lucky prince? Gentle physician? Ice-cold mystery male? Who is her true love? Haha, but she only eats, definitely will not take responsibility! Beautiful men be careful!

- Description from Novelupdates

The moment when mercenary leader Kwang Hwi receives video game like abilities, the world is suddenly thrown into chaos. A thick fog envelops the Earth, bringing with it savage, otherworldly monsters. At the same time humanity has been rendered defenseless against this onslaught, as the strange fog turns most weapons to rust. With mankind spiraling towards oblivion, it is up to Kwang Hwi, with his new abilities, to save the world. Watch as Kwang Hwi leads his militia and becomes the last bastion of humanity. Will he be this world’s savior, or its conqueror?

A lonely soul, which was placed under the care of the Lord Protector’s Manor, ended up having her lover stolen by the family’s eldest daughter and dying tragically the day before her wedding.

Somehow, she was reborn in the family as their 14-year-old first wife’s daughter, Ning Xueyan, with a startlingly familiar face.

Step by step, she will ruthlessly scheme to seek revenge as well as uncover the mystery of her tragic death.

Her former fiancee, the flirty crown prince and the bloodthirsty prince, will now bear witness to a vengeful Ning Xueyan becoming the peerless lady of her generation…

Waking up from a hangover, Wang Hao finds himself reborn in an alternate world. To his delight, he realizes that he has a system to help him in this new world. However, his system turns out to be a highly unconventional one. Instead of serving justice and winning the respect of other people, Wang Hao has to do all kinds of bad things in order to make use of the system. So, Wang Hao embarks on the journey to being cursed for good…