Choinui Game Bangsong

Uhyeon Baek logs into Reverse Planet expecting a VR game, only to discover that the world is painfully real. A decade of grief and experiments turns him into a superhuman contract killer, and he finally executes the director behind his suffering. But when he returns to his original life, the ghosts of his fallen companions follow him. Haunted and restless, he goes back to Reverse Planet, only to realize he's entered the real game this time. Paired with superstar streamer Soyul Kang, his lethal efficiency goes viral... and puts him on the conspirator's radar.

(Source: WEBTOON)