While in Gotham with Durselys on a business trip. Harry gets taken in and adopted by Bruce Wayne.
-Harry becomes a Robin or you can make up a sidekick name so he fight along his adopted family.
-The magic world find out about the adoption and try to bring Harry back the England but can't.
-Sirius does get sent to prison but shortly gets a trial and gets free after the adoption.
-Harry get trained in magic by one of the magic heroes of DC so it won't get out of control.
-The Order years later goes to Gotham to try tell Harry that Voldermort and his Deartheaters are back. But get mixed up in the events of the craziness of Gotham life. Both the good and the Bad.