Rebirth of the world strongest weapon user

Rokki is a loser in his school and in his entire life. He got pushed off the roof by the bullies and he died because his father refused to pay for his treatment. After he died his soul got swapped with a boy name Lexus and he was stuck in another world Lexus was the strongest weapon user feared by all in his school. He was murdered and his soul becomes a ghost that can only be seen and heard by Rokki Together they are forced to cooperate and adapt to this new world. Lexus last desired is to make Rokkie becomes the strongest and to find his murderer