Toaru Majutsu no Index: Genesis Testament - Volume 3, Chapter 4: The Demon Lord’s Young — the_LIGHT.

Third Miss Luo relies on her father’s power to create chaos everywhere and is notorious for bullying the weak. When she had nothing to do, she led a group of servants to the streets to flirt with beautiful and handsome boys. For Princess Qingyang, if this kind of person dared to behave wildly in front of her, she would just kill her with a single finger—until she opened her eyes again and found that she became Third Miss Luo, Luo Sheng.

- Description from Novelupdates

In childhood, they were neighbors. Xie Zhen always bullied Li Yu.

After years of longing, Mu Chenyan was finally going to marry the man of her dreams — Yuan Xuan. However, on her wedding day, the tragic death of Shu Qinger, her well-known romantic competitor led to Mu Chenyan’s prison sentence.

Kai is the hardest working warrior in his generation... and the unluckiest. In a world where most people receive magical skills, classes, or cultivation, Kai has nothing but his wits and his strength. His only choice will be to forge a new path against fate, no matter where it takes him.

Savage monsters pour endlessly from the wasteland, threatening the survival of civilization itself. They say that human strength isn't enough and only those gifted with destined powers have a chance of making a difference. Kai is hungry to fight in that war, to be someone who matters. That hunger will take him across a world stranger and more terrible than he could possibly have imagined.