WARNING
UNTIL THE HOGWARTS ARCS, MOST OF THIS IS REALLY SHORT WITH SMALL THINGS HAPPENNING. IT MAY QUALIFY AS FLUFF, BUT I'M NOT SURE.
"And this is where I store cubes. Companion cubes, weighted cubes, cornerless cubes." GLaDOS explains, showing Harry the cube storage. "This, however, is the development chamber." She continues, opening a door to a solid white room, in stark contrast to the solid black storage area. A cube floats around randomly, bumping into walls every few seconds. "This is the Anti-Cube. So far I've only made it as dense as air, so it just floats. Nothing else, ever."
"Dense?" Harry asks, wearing his brand new orange Aperture Science Jumpsuit™, and tilting his head slightly. GLaDOS turns one of the cameras to him, and explains, "Density is how much stuff is in a space. This cube is as dense as air, which means it weighs as much as that much air, which is why it floats around instead of falling through like we, the denser objects, would." Harry looks at the camera and asks simply, "Then why not fill it with something less dense, so the air falls?"
If GLaDOS had a face, it would flush with embarrassment. "I... I am embarrassed to admit that I had failed to consider that..." A robotic arm reaches out into the room and grabs the cube, pulling it into the wall. Several mechanical sounds like a buzz saw are heard, and the cube pops back out of the hole in the wall, which seals itself up, and the cube floats to the top of the room about as quickly as a normal one would fall. "Thank you very much, Harry."
Harry giggles at the praise, and responds kindly, "You're welcome, Miss GLaDOS!" Some beeps and alarms sound, and GLaDOS excuses herself, "I'll be right back. I have to go see what this is."
GLaDOS, focusing on the camera outside the entrance, finds two strangely dressed humans. Both of them are pale, both wear robes, and both seem out of shape. She directs a camera into their faces and commands the newcomers rudely, "Go away. We are busy testing. If you have any inquiries about exactly what we are testing, then you'll have to become part of testing. Once you become part of testing, you never get to leave. Therefore, unless you wish to spend the rest of your worthless lives placing cubes on buttons and being shot at, go away."
The newcomer on the right responds just as rudely, in a deep, gruff voice, "We are aurors, here for Harry Potter. He has been illegally taken from his home with his aunt and uncle, and he must be returned immediately or else we are authorized to use killing curses." The camera GLaDOS controls does not move, but the sound of an elevator moving is heard almost immediately. Both aurors smile at their triumph... only for the door to swing open hard, knocking the left auror unconscious, and revealing a small white oval robot, who says in a childlike voice, "Hello!" and opens fire upon the two.
"What was that?" Harry asks as the alarms and beeps turn off, and GLaDOS responds simply, "Loiterers. Anyway, I was thinking maybe you could help me design some tests for Atlas and P-Body until I come up with some new test element."
The next few hours find Harry and GLaDOS putting together a large tunnel with buttons on the ceiling, each which opens a door to a separate tunnel, some of which having turrets, some of which having more Anti-Cubes for use, that kind of thing.
This is put slightly on hold as Harry's stomach rumbles, cutting him off as he describes an idea he had for a new testing element. "You can tell me while you eat, Harry." GLaDOS states simply, using a vacuum tube to give him a small plate of hash browns and a fork.
Harry starts to eat somewhat slowly, as he tries again to describe it, "It'd be like a cube, except big enough to put a portal on, and it be a... what did you call it?"
"A portable surface?"
"Yes, that's it! It'd be a Portal Cube! You could put a portal on it, and use it to move around the bridges, and the lasers, and the bombs, and all the other stuff in tests, instead of just the lasers with that other cube..."
"The Discouragement Redirection Cube?"
"Yeah, that one!" Harry jumps up and down in excitement while GLaDOS nods the camera she currently inhabits, and the two quickly get to work on designing more tests while GLaDOS sets up the factory to start making Portal Cubes.
'What a smart kid.'