Thought blurb:
Akira/Harry Potter Cross. Either a) voldemort or b) harry potter or c) both! were cut up and dissected at some point and preserved in cryofreeze individual little jars when it became known that the war was ongoing by the muggle population.
London goes up in a ball of white. 25-30 years later, after the third world war ends, and London's a mess. Where the center of London used to be, a large brackish lake now exists. Magic is practically non-existent, a bulk of the wizards and witches having died during the unexplained explosions that triggered WWIII. Those who remain are broken and essentially have lost their magic, or are carefully guarded prisoners of the state, as the state attempts to unlock the secrets of magic.
Enter a group of kids – likely descendents of the great wizarding clans – they are the descendants of the Potter, Weasley, Longbottom children at the end of the 7th book. The kids survived the great catastrophe, but lost their parents, and lost their magic. They stayed close together, and their children have turned into hoodlums, lost in the post war reconstruction and degradations. One of the kids has an encounter with an escaped mage (Ron Weasley and Hermione Granger in the role of the test subjects) Frightened, the mage performs some wandless magic, sending one of the kids into a government hospital. Tracks partly with the events of the AKIRA series, as the government is intent on unlocking the secrets of magic. The kid (probably a Potter?) tries to rescue his friend (a weasley) from the government facility. The Weasely has been fed lots of hallucinogenic drugs, causing him to freak out and start with the wandless magic. Turns out a family that supported Voldemort is on the government side – and like the others, he's lost his magic. He is not ignorant of his heritage and is eager to reclaim it.
The hospitalized child's magic is going out of control. He seeks the cryofreeze where potter is frozen in little jars. His magic makes the freeze cycle end, and all the little jars float up to the top. They break, but the child's magic can't reassemble them into a real human. Magic flaring wildly, the child loses control, and starts morphing wildly into various magical creatures. The Potter orphan tries to help, but is losing the battle. Eventually, Harry Potter eventually reappears, along with his two friends, Hermione Granger and Ron Weasely. They do the mass wipe spell again, and the young out of control mage is sucked in, and the young Potter transported out.
The spell wipes out a great deal of new London, but also resets magic in the world. There was a great imbalance, and that is what caused the young mage to lose control. The Elder potter appears before the younger in his mindscape, and gives him some commands to restart the world of magic. When he reappears in the real world, he finds himself standing outside of the abandoned Hogwarts castle. It jumps to life at his presence, and he walks into the castle halls, eager to learn about this new world he's inherited.