This is after Ben 10 Alien ultimate arc.
Ben lost his friends and family to Vilgax after a tiring battle he won realizing he has nothing left uses Alien X powers to transfer into another universe he lands in a alternate earth (Highschool dxd world) Ben Tennyson decides he wants to start a new life and try to forget his past with a new name issei hyoudou at the time goes by through the Riser Arc issei wakes up and find out they lost the match against riser angry at himself for feeling useless decides to put on his Omnitrix to save Rias as a hero he meant to be. Harem
Also Ben/issei also has the boosted gear.
Just imagine four arms or waybig with balance breaker scale mail.
