Novel and ff ideas for authors

Twins suddenly got transported to another world and gained many overpowered abilities as well becoming apprentices or desciples of the demon lord, and they only returned because they were killed by the hero and his party to kill the demon lord. But they were suprised that they returned to earth their country was already destroyed. Because of the monsters but they didn't believe it so they enslaved all the monsters in their country, especially the strongests monsters residing in their country and when they found out that it was not the monsters fault, that their country was powerful but easily got destroyed by a very powerful monster, when they heard everything from the monsters of what happened they became angry and vowed to take revenged against the entire world as other countries didn't helped their country fight back against these monsters. As the apprentices/desciples of the demon lord eating human meat was a common thing as demons see humans as food and so do the two of them, and because of the demon lord they see every being beside monsters and demons as food and nothing more. But they still love their country and their parents so if they found their fellow countrymen they will treat them as family.