DISCLAIMER: Everything here does not belong to me, only the plot does. All characters here belong to the amazing Hideyasu Takahashi. All the pictures belong to their respective artists but I mostly get the pictures from Google Images.
WOAH! ANOTHER UPDATE IN ONE DAY?! IMPOSSIBLE!! All joking aside, feel free to use this idea. :))
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What if, all this time, Joker was a kid
In this AU, Joker is either, at least in this AU, canonically short ("I am not a kid! I'm just fun sized!!!) or maybe there is technology so advanced that it can make something like the Kage Bunshin no Jutsu (Shadow Clone Jutsu) from Naruto.
One day it was revealed to either the usual gang (Hachi, Spade, Queen, Silver Heart, Shadow, Rose, Akai, maybe even Oniyama and/or Ai) or to the world, like, they don't know his identity but know that he is a kid (News Flash: The infamous mysterious Joker is a KID!) ((A/N: Kudos to you if you get the reference))
He either gets coddled by everyone ("Make sure to be back before midnight!!" "You absolutely cannot go outside tonight!" "JACK JONES YOU GET YOUR ASS BACK HERE IN THE SKY JOKER YOU WERE GROUNDED FROM THE LAST HEIST!")
Or people degrade him, try to make him quit ("You're just a kid, you're not fit to be a Kaitou! So give up!" "I can't believe I trusted a kid! Kids are so irresponsible and selfish!")
Honestly, if you couldn't pick it up from the last two paragraphs, this could go in many different ways. Like how if you choose the latter from the above Joker can become depressed or rise to the top and surpass everyone's expectations.
Or you can disregard everything except the first paragraph and write all about his adventure on trying not to get caught.
Or you can also do whatever you like!
That's all :))