The world, and it's people, all greatly changed, ever since superhuman abilities became common place.
Larger-than-life heroes, the dastardly villains who opposed them, world-ending and life-saving Quirks, all intertwining and clashing against one another on a daily basis. Coupled with all the new laws, regulations, customs and restrictions, this "Brave New Heroic Future" of ours was a cocktail of chaos that was bound to make one's head spin.
And then, there was you. All and all, an average Joe. You know the type, average height, weight, the most boring hair color you could think of. Truly, with no real special traits to boast about.
Well, apart from your Quirk.
Your luck, thankfully, wasn't terrible enough to make you Quirkless....buuuut compared to other "gifted individuals", your power kinda' sucked. Forget All-Might's Super-Strength, Hawks' flight or Endeavor's Hellflame, no no. Your mind-shattering, world-changing, career-defining ability...........
............was to shrink.
Yep. You could shrink from your current height of 5 feet and 8 inches, all the way down to around 1/10 of an inch, though, such a rapid shrinkage would be taxing and leave you unable to regain your former height for quite some time.
That was the second part of your Quirk, the ability to grow back to your original height.
The more reduced your height was, the more dense and durable you became, almost to the point of being as hard as a diamond. However, the practical application of this durability would be reduced, due to you having to be the size of a grain of sand for it to take full effect.
It wasn't the greatest of abilities, but at least your head wasn't a pencil eraser or your hands a pair of cactuses. And, you made it work quite well, considering you were......