In previous chapter of story nobi nosuki get transferred in different world but after when a demi human girl died in his hands. he decided to free all of demons from Labour. and after put that demi human into grave. nobi nosuki notice something in front of his body that's the control system in that he have unlimited magical power, unlimited straight power, unlimited diamonds and now he get power to summon demons and sprits for himself. and after that nobi nosuki understand that what he have to do then he decided to become demon king!
and after all of that nobi nosuki notice that he is in game world because he have that kind of game control system with special ability that which with he sit he get the all of their abilities to like that demi human ability he get from her because he hold her for some minutes until the end of her. and after nobi nosuki called the previous demon king and asked to him why all demons now slaves of these cruel humans then previous demon king replied to nobi nosuki that he defeated by a hero and that hero is the most cruel to be called as hero. hero killed him and all people started to think like us unwanted stuff which born only for to work for them to end of our life's. then nobi nosuki replied to previous demon king that he will change everything and said to previous demon king that i nobi nosuki now will be called demon king. after nobi nosuki asked to demon king about how to set up again demon Empire then previous demon king replied to nobi nosuki that go and find some of his previous friends they working to stand again to demon Empire then nobi nosuki asked to previous demon king how can i find them if i find them then they will accept me as their king then previous demon king replied to nobi nosuki that i will give the treasure of mine who have that. that only person will only rightful to be demon king and i think that only you have that kind of power and straight who can able to stand the demon Empire again and make every demon free from these cruel people.