Hareluya 

It is the manga Umezawa made before his very succesful follow-up BOY and which tells of the adventures of Hibino, delinquent son of God. God gets enough of his son's behaviour and sends him down to earth to better his life and test him. The outcome of this will determine the future of the world, because God won't have his son succeeding him if he doesn't better his life and will end humanity if Hibino fails.