A/n: Here's part 4, I hope you enjoy!
"Oh, it's amazing what a little pickpocketing can do, Weasley." Draco smirked as he dropped the book to the ground as he approached.
"The book!" Harry gasped; his previous embarrassment gone.
"You stole it!" Hermione yelled.
"It's not my fault you weren't paying attention." Draco retorted, stopping as he stood in front of Harry, staring down with a smile as Harry looked up to him. "Little Harry, a shame you aren't a grown man like me."
"Why did you do this Malfoy?" Ron spat.
"What else?" Draco replied as if it were obvious. "To prove that I will always be better than you."
It was at that point however that Harry grew again as his body slow rose, Harry suppressing a groan as he did so, up until it was he who was staring down at Draco, standing at a massive 23ft in height. "I-I'm...ngh, look. I am growing Draco, taller...gnah...than you."
Draco simply huffed.
"This is better you know." Draco suddenly spoke up. "So...gnh, so much better."
As he said this, his body expanded further as he slowly grew up to Harry's height, both looking at each other in the eyes as Harry looked at him quizzically.
"Better?" Harry asked. "How is this better Draco?"
"Because Harry..." He smiled. "We can rule all of Hogwarts, the world even."
"W-what do you mean..." Harry pressed; his eyes narrowed.
"With us being giants, everyone will be afraid." Draco answered simply. "You could crush those in your way, stomp on those you hate."
"I-I don't-" Harry began, but Draco cut him off
"Think of it Harry, we could be unstoppable." Draco interjected.
Those words made him think back to the Dursleys, how he felt powerless against them and how he wanted nothing more than to pay them back.
"Don't listen to him Harry!" Hermione yelled.
"I-I'm sorry, b-but this is just too good to pass up." Harry stated.
After those words were said, Draco and Harry's bodies began to shake as the began to grow once more, Harry's boxers being shredded to nothing as his penis lay dangling out for the world to see.
They were now a whopping 28ft tall and Hermione and Ron's expression was that of shock.
"Yes Harry, look at this power Harry." Draco grinned. "We're unstoppable, now let's go show everyone who's in charge."
They both left, their footsteps causing the ground beneath them to rumble slightly, their toned bodies heading to the castle.
"W-we need to stop this." Ron stuttered.
Hermione did nothing but nod.
They needed to make the potion first, then deal with Draco and Harry.
A/n: How was part 4? It seems like the bigger you get, the more the power corrupts you.