The Curse of Desire - Chapter 30: Best Friend’s Brother ()

Zhang Gong decides to learn light magic, a magic few show interest in and eventually becomes the legendary Grand Magister. While trying to end the continent’s east and west separation in order to unite all of the different races, he becomes every race’s Child of Light.

King Grey has unrivaled strength, wealth, and prestige in a world governed by martial ability. However, solitude lingers closely behind those with great power. Beneath the glamorous exterior of a powerful king lurks the shell of man, devoid of purpose and will. 

Reincarnated into a new world filled with magic and monsters, the king has a second chance to relive his life. Correcting the mistakes of his past will not be his only challenge, however. Underneath the peace and prosperity of the new world is an undercurrent threatening to destroy everything he has worked for, questioning his role and reason for being born again. 

She, a genius abandoned by her clan. He, a proud, pampered, two-faced imperial crown prince, a developing supreme ruler of the world. She, tricking him, disguised as a pig to eat a tiger, suppressing him, provoking him. Every time, after playing with him and stirring him up, she’d escape.

No man could put up with this! He could only hunt her, pamper and indulge her, lure her into falling in love with him, who would have thought, the one to first fall in love would turn out to be him———-

A young man who stood above the world, a young lady who dominated the landscape, evenly matched opponents, evenly matched romantic game of chase and tag.

- Description from novelupdates

There was a Senior Brother and a Junior Sister. One of them was transmigrated to this world and had cheats while the other was the reincarnation of a Great Emperor.