reika's manga / #supernatural(817)

Yeon-Woo has a twin brother who has been missing for years. Their sick mother ends up dying and leaves him alone. He suddenly receives a mail informing him that his bro had been alive all those years doing adventures in a game like world. At first for medicine but he loses track of that goal somewhere along the way until he loses all his battle companions in that world and is backstabbed and killed by them. Yeon-Woo devotes his life to avenge his brothers death and finds the world his brother was talking about. Now all that's left is to find the assholes.