King of Assassination: searching for Queen

A man transmigrated to immortal world, full of God, demon, beasts, elf, dragon and many other beings. He reborned in the body of a good for nothing man in the weakest part of immortal world known as disolate West with a system which helps him in becoming world's strongest assassin and to form world's strongest Assassination organization. Just in Five years he completed all the mission system provided him and became world's strongest Assassination and also Patraich of world's strongest Assassination. Now, he has two identies first Marks William, the son a elder in William family in capital city of Rodelph dynasty and second THE Emperor, world's strongest Assassin. This story began from the point where system gave him last quest. Quest: King's Heir Objective: search for the next inheriter of the system. Reward: Organization Management system remained with you. Failure: complete shut down of system.