A few feet

You feel dizzy for a few seconds, and, next thing you know, everything around you is suddenly much taller, especially Touka. She bends over and eyes you with a scientific curiosity, making her huge breasts (which look enormous to you now) hang in front of you. She smiles, "Well, well, it looks like the serum is working properly as planned. If I had to guess, I'd say you'd already lost a good three or four feet from just that." Touko might be enjoying this, but you're certainly not. You freak out as you realize your clothes no longer fit you. You look more like a toddler trying to put on his dad's clothes.

As you struggle in your now baggy clothes, Touko says, "Hold on, Tommy. I think I've got something you can wear right over here." She rummages through a nearby drawer and pulls out a pair of purple kids wrestling shorts. You'd question why she has those, but, to be fair, that's far from the strangest thing that's happened today. "Try these on," she says and hands them to you. She looks away but gives a sly peek in your direction while you change out of your baggy clothes into the shorts, making yourself decent again. To your surprise, they're a perfect fit. "See," she says, "Do I know how to take care of my wrestlers or what?" You roll your eyes at the woman who put you in this mess to begin with."Oh, one last thing you should know, Tommy: based of my findings when I was first making the serum, I theorize that there are certain instances in which your body could potentially accelerate the shrinking process, with the risk increasing the more those instances happen. So, you know, you should probably be careful at your new size." Understatement of the year.

A brief pause. "Well...are you going to tell me what those 'instances' are," you ask.

"Nope"

"Why not?"

"Cause where would the fun in that be?" You give an aggravated groan.

"Oh don't be like that, Tommy. I'm sure you'll figure out the full extent of your shrinking condition on your own, and, that way, you'll really own your new tiny persona. Tell ya what: to help motivate you more, I'll make sure to have some the antidote whipped up by the end of your first match. If you win, I'll let you have it, and you'll get some of your size back."

"B-but, how am I supposed to beat anyone at this size," you desperately ask.

"That's for you to figure out, little guy. So, now that things are settled, I think..."