Here, have a Harry Potter Gintama crossover. Hey, I've gotten a plot bunny out of my head! This a miracle! This'll be cross posted onto my Wattpad account so don't report WritingIsMySoul if you spot the story on their account, because that's me.
Gintoki blew the dust off the cover of an old book, trying not to sneeze, as practical mounds of dust had flown off of it. Examining the spine(which read Fantastic Beasts And Where To Find Them,) he decided it might be important and tossed it haphazardly into a nearby trunk. Shinpachi, who had been elbows deep in another pile of books immediately protested. "Ah, Gin-San, don't just through the books in there to carelessly! Who knows how old they are."
Gintoki waved him off, "Can't be too important if it's sitting in the attic. Like those comic books your grandma keeps in her attic but never does anything with."
Kagura chimed in from over a pile of boxes, "Old geezers don't understand the value of comics, aru." "Oi! You calling me old?"
The trio were in the attic of a client, an old geezer who had requested help with packing his trunk. He had mentioned something about Hogwash and a Dumb Door, before hurrying them upstairs and telling them to fit everything they could in the biggest trunk they could find.
So far, it wasn't going well. Kagura had started cramming the biggest items she could into the trunk they had found, causing it to bulge outwards, much to Shinpachi's dismay. The bespectacled boy had to pull the boxes out, and attempted to organize it, which wasn't easy when Gintoki tossed whatever looking important into it. Eventually he had given up, and the trunk was a haphazard mess.
Turning away from a large, unused cage, Gintoki had his attention caught by a large cloth covered object, looking to have been hastily crammed in the darkest corner of the attic. Something about it seemed to call to him, and slowly he reached out, fingers brushing the curtain before grasping it and pulling down.
It was a mirror. But not a normal mirror, because in the reflection, Shoyō stood behind Gintoki, with Katsura and Takasugi. Takasugi had both eyes. Sakamoto, who was farther back, had his forearms exposed, and the wound that had crippled him as a swordsman was gone.
Whirling around, the space behind him was empty. Turning back to the mirror, reflection Shoyō was smiling, while reflection Katsura chatted with reflection Takasugi. Reflection Sakamoto simply laughed. A genuine laugh, and though there was no sound Gintoki could tell.
Cautiously, he raised a hand to brush across the dusty surface-
"Gin-San, we finished packing!" "Cmon you geezer!" "Yea yea, I'm coming... Brats." The end of that sentence was mumbled, and as Gintoki looked back in the mirror, it was blank. Shaking his head to clear it, he moved away, scratching the side of his head. How strange.
Just incase you cant tell the mirror is from the first book. Or maybe the second. Can't remember.