So the story is that Ash Ketchum is betrayed by everyone, and everyone means every single one. Be it his friends, Champions, Elite Four Gym Leaders, Legendaries and even Arceus himself.
After his brutal death, Ash was transported into the World of Highschool dxd.
Couple of points:-
1) Issei is female in this fanfic.
2) You can suggest Ash's Harem and his Aura Powers.