I already did one of these for a more multiversal oriented fan fiction idea, however this idea is instead just Bleach and DxD. I was thinking of maybe a combined world of the two series, where Shinigami and Quincies are isolated pantheons, and Ichigo discovers their existence after the Thousand Year Blood War when he decides to take a vacation to Kuoh Town to relax after the war. I don't want him to become a devil, but I do want him to have mutated evil pieces for himself and his friends. These evil pieces would be known as 'spiritual pieces', 'Shinigami pieces', 'soul reaper pieces' or something to that effect, and they would be developed by Kisuke. I want his group to go on a completely separate journey from Rias and her peerage and make their own name in the various factions, and only then have Rias and her peerage introduce themselves into the story later on after they're sufficiently powerful and have obtained a decent amount of fame. Have Chad, Orihime, Uryu, Kisuke, and Yoruichi in Ichigo's group, and then have anyone else you want added to the peerage, maybe characters from different pantheons and such. I also would like for Issei to become part of Ichigo's group rather than Rias's peerage, and for him to join willingly after being told of the various females he would likely meet along their journeys. Eventually, I would like it if Issei's perverted nature gets turned down a little as he experiences more of what the world of DxD has to offer. I also want him to have true Bankai Zangetsu.