Avatar: Mage of All Elements - Chapter 48

This story is centered around the man named Yi Ji-Hyuk, who has spent 1000 years in a Medieval Western fantasy-like world before returning back to the modern-day Earth. When he returns, he finds that his home is facing monster threats, and that humans with superpowers have appeared to protect the innocent people of Earth.

A protagonist reborn in another world.

Pinning her tall body against the hard wall, he looked into her beautiful emerald green eyes as he spoke in a deep voice, "I have two options for you," his body came closer to hers as he continued, "Be my girlfriend. Or," his lips turned into a sly smile as he whispered close to her ear, "Be my boyfriend." He even dared to wink right before her as his dark orbs glinted amusingly.

He, since childhood, had followed the Foreigner to practice the Defying Heaven Art, entering the most secretive special forces and becoming a fearsome assassin that made others tremble at the mere mention of his name. After a single failure, he took early retirement, but he ended up as the personal bodyguard for a rich heiress, a school beauty. Accidentally provoking some mysterious Cultivators, he gradually unveiled a hidden world of Cultivation beyond the mortal realm...