Ultimate Highschool DxD

In the future,

Issei got married to the girls and had many children. But suddenly, one day the seal on Trihexa broke. He was released, along with Sirzechs, Falbium, Serafall, Odin, Azazel and the others who were also sealed.

All the races and mythologies went on a war against Trihexa. But no one could defeat him.

Atlast, by Issei's request Ophis and lilith also fought Trihexa. Lilith merged with Ophis and Ophis fought Trihexa at her full power. She defeated Trihexa, but due to their battle all of space-time got destroyed.

The entire world was destroyed and even Ophis was destroyed.

In the end, the Great Red survived and managed to save Issei. Seeing everything and everyone dead, a hidden power unlocked in Issei. He remembered his past. He was actually a pure blooded devil. He had the power of Agares in him. Using it, he went back in time. On the day of his birth in the underworld. To know his true identity and to save the world from Trihexa and to protect his beloved Rias and fiancees.