The promise

So this story starts in a city on fire with a huge fight going on between a caracter that seems to have supernatural powers like bending the lightning and using some kind of god like techniques(majestic golden flames start to light up from his fist and sword).

And his opponent is the devil god himself even between the devils and demons the strongest one out there in this wrold. It seems like the devil god has the upperhand because of his overpowerd dark techniques but somehow our character escapes but with major wounds but he goes to his sons and to his wife and he hugs them and using the power of lightning he wants to teleport them to his father wich lives in a village on the mountains but his wife and his biger son starts cring and panicing that without him they cannot survive but the dad says that he needs to sacrifice himself for the sake of his Nation and that his heart is broken into millions of pieces that he cannot go and protect them and to see his sons who he loves more than his own life grow up but in tears he uses his powers to teleport them to safety and he goes back to face the demon God and they start to fight again.

And then we can see that the rest of the family wher the biger son is the antagonist of this manga as they meet the grandfather wich name is Isogita Yakadon and he is prety much reliefd that he can see his grandchild's without any harm and he knows that his son has the power to defeat any kind of opponent but when he finds out that the opponent is the devil god himsefl he knows that he cannot escape alive because even the strongest God's cannot defeat him so he organizes the funeral for him they all take a goodbye from him but our main character wich name is Edymaro Yakadon makes a huge promise that he is going to kill all the devils and demons in our world and after that he will search the demon king and give him the most painfull death.

After 1 week there comes the confirmation that the  8th King of Lightning, Yakaza Yakadon has given his life to seal the demon king in a lost dimension from where even him can't come back to hurt the humanity but he left all of his slaves on our wrold in random places but in every corner of the wrold to grate him when he is going to come back to this world.