Science fantasy AU where magic is a thing. There’s several types of spells; permanent spells, which remain on the target, affecting it, until cancelled or until they wear off, and instantaneous spells, which, once done, have to be counterspelled. Permanent spells lack proper ontological inertia; removing a permanent shrinking spell will cause the target to grow to their true size in a few seconds. An instantaneous shrinking spell cannot be removed so much as countered (it’s done its effect, it’s finished and gone) and once done, have ontological inertia. Hiro and Tadashi have magic ability and both have minor magic surges.
Magic surges result in wild magic that can do things that human mages then can sometimes take years to develop ways to replicate-most spells were copied from the effects of magic surges.
Hiro’s are stronger overall, but as he has the potential to be a VERY powerful mage, it’s to be expected; they mostly just levitate objects, make random things glow or change colours or stick to each other, and are easy to handle by whoever’s not surging (this includes Aunt Cass). The effects of both boys’ surges are easily reversed, or naturally wear off in a small period of time.
Then they discover the hard way that a then six-year-old Hiro’s peanut allergy includes the bizarre (and reasonably rare) symptom of ‘powerful magic surges’. Opps.
It’s very difficult for Cass and Tadashi to reverse and manage the effects of the surge, and while trying to corral an animated table that had sprouted claws and was taking swipes at Mochi and the walls, they fail to notice that Hiro’s shrinking.
He stops at the size of a large mouse, and it’s an instantaneous spell.
The first day’s the hardest; they have to adjust, and quickly.
By the second day, Hiro’s got a warming spell on him, keeping him at a comfortable temperature, and a simple weak protection spell that made him slightly tougher and stronger.
By day five, a professional mage had boosted the protection spell until Hiro was twice as strong, and tough enough to survive being stepped on. (A Lucky Cat customer with poor eyesight thought he was a mouse and tried to squish him. )
Aunt Cass starts homeschooling him, and getting in tutors to help; meanwhile Tadashi sews Hiro brightly coloured clothes so that Hiro doesn’t get mistaken for a mouse again (splinting a broken arm the width of a toothpick is HARD).
When Tadashi graduates, Hiro insists on going to SFIT with him-as in, riding in his pocket.
Not having been bullied as much as canon Hiro, this Hiro is much less nervous and insecure, and so doesn’t fake confidence.
The first people he has a proper chat to are the Nerd Herd, who he meets because they’re sharing a lab.
(Fred will forever deny squeeing at the sight of a kitten-sized 13-year-old kid sitting on Tadashi’s hand and smiling nervously up at them. )
They quickly become friends.
Submitted by: Longpost Anon
(Awww, I’m basically picturing the scene in Cinderella where she makes tiny clothes for the mice. Only Cinderella is Tadashi, and the mouse is Hiro. I bet Tadashi goes out to fabric stores with Hiro in his pocket, and they pick out the craziest, brightest, funnest bits of fabric from the scrap bin for super cheap, and take it home and just go NUTS with it. Hiro probably has a lot of really wacky ponchos from when Tadashi was just starting out and learning to sew
If he ever grows back to normal size, he will definitely end up still wearing wacky coloured things. Because that’s what he’s used to.)
