She uses it on her shoes.

She grabbed a few Upgraders and click-clacked her way to the bench, breathing deeply.

"Now, how do I use them? They won't fit in the keyhole."

The girl noticed that the front end of the cylinder was flexible and figured that she could apply it to any part of her outfit. She took one of the Upgraders and was about to find a place on the swimsuit to use it, but suddenly stared at her shoes.

They were undeniably beautiful, but Jen's feet were quite sore underneath, and she ultimately decided to try out the mysterious device on them first, holding the rubbery end of the cylinder against the keyhole on her right ankle. A green rectangle started glowing on the side of the device, and it started pumping the substance right into the strap. When it became empty, it fell off on its own.

For the next few seconds, nothing happened, and Jen was holding the second one above her metal crotch, using last shards of her patience to finish the 'test'.

Then she felt and saw her shoes changing their appearance. White leather started extending both down and up from both of her ankles, covering more of her skin.

"No, no, no, what the fuck?" — the girl witnessed the liquified material join together over her feet, transforming shoes into boots. The heel and platform became higher and narrower, reaching seven and a half and two inches respectively.

After extending the shaft to three inches above the strap that now had two keyholes instead of one, it stopped, leaving Jen with a dilemma.