Jobless Reincarnation - Mushoku Tensei - Chapter 12: Separation

The ill-fated high school student Liu Yuan obtained the inheritance of the top civilization in the universe and changed his own destiny. He also used many powerful technologies in the inheritance to lead the Chinese nation to rise in the universe.

- Description from novelbuddy

Flatten the Devil's Palace, eradicate the demonic cult, slaughter the demon lairs, sweep through the demon realm, dominate the heavens and earth, control the three realms, be the supreme master of the mysterious sect, master of the Nine Yin, the 17th head of the North Star Sword Sect, the Heavenly Fiend Lone Star, the Supreme Sword Soul, the Supreme Infinite Mysterious Heavenly Wishful Great Sword Patriarch... Also known as Iron Egg, known for the wild history of relentless killing.

Two years ago, the mere fifteen-year-old scion of the Lin family, in front of the colossal behemoth that is the Murong clan, made a vow!Two years later, no one knows what he has gone through, but from the moment of his return, he radiates a brilliance that seems to compete with heaven and earth!(Note: The protagonist of this book is very aloof, cold, and passionate. Those who like to read about a military king's ambiguous romances and flirts, please bypass this one.)

The story is about a boy entering high school, who answers a strange call from a public phone one night. The caller challenges him to a bet: She’ll remove the birthmark which he sees as the cause of so many problems, and he’ll have fifty days to win the heart of a girl he’d considered far beyond his reach. And with this, a very strange summer begins.