Black Blade Zero

Ryuichi Yamamoto, the commander of the United Nations Special Forces Black Blade, is known as the "World's Strongest Man." During one mission, he was shot and lost consciousness. The next time he wakes up, Ryuichi realizes that his soul has transferred to his younger brother Ryuji's body.
My own lost body, the soul of my missing brother. Pursuing the truth, Ryuichi steps into the darkness of the city. However, what is revealed is a national conspiracy in which the younger brother was involved, and an illegal human experimentation plan that was being carried out in secret.
As Ryuichi regrets his past choices and engages in deadly battles against powerful enemies, a mysterious woman, Miyuki, appears, identical to Kosame, the beloved woman he once risked his life to protect. Her true identity and "Country X" that operates behind the scenes of the world. A dark military action game where fate and violence intertwine.

Original Webtoon