Issei's destiny was to become the king of the harem, but because of a very bored old man who accidentally put a magic circle that would change the lives of the Issei in a way that he himself could not wait.
I am not entitled to the Fate or DxD franchises.
PS: this story is planned to create something that almost new could keep the main story, but there will be great changes, such as putting more importance on the characters who died or are almost unknown, or factions that almost do not join the main story.