Transfixed, Harry stared half in horror and half in morbid fascination as Oleandra slowly pressed her hand through Umbridge's head. At first, nothing seemed to give, but little by little, Oleandra's fingers penetrated the toad woman's skull, like a hot knife through butter.
"Wha… what are you doing to me!?" Umbridge screamed face down into the floorboards. "Stop! Stop this at once! I order you to stop!!"
Gradually, Umbridge's annoyingly high-pitched screeches turned into frantic screams of terror— she could feel Oleandra's hand rummaging around the inside of her skull, touching things it had no business touching.
"Ah, yes…" said Oleandra softly, as if enraptured by whatever it was that she had grabbed hold of. "So, is this what you care about the most in this world?"
"No! Don't… Don't touch that!" Umbridge shrieked, her eyes bulging like a toad's. "I am Dolores Umbridge, Headmistress and High Inquisitor of Hogwarts! You do not have the right, you filthy, base, creature! You are beneath me, you Half-breed! Don't you know that I'm Senior Undersecretary to the Minister of Magic!?"
When Oleandra's Fairy Magic had brushed against the core of her very being, Umbridge had somehow caught a glimpse of Oleandra's true nature. Instinctively, Umbridge knew just what kind of fate awaited her; she had touched upon the truth, and it was too late to stop what was coming.
"You care for nothing and no one but yourself, Dolores Umbridge," Oleandra's thundered, as the pitch of her voice shifted and multiplied into a choir of a thousand different women's voices. "You see those who are not like you as unworthy of life itself. Muggles, Muggle-Born, non-humans… Your magic, pathetic as it may be, does not make you any better than those you've deemed inferior. How you can take pride in such mediocrity, I will never understand."
"No…" Umbridge mumbled incoherently, her eyes rolling upwards into her skull. "If you… I'll be… no different…"
Slowly but surely, Oleandra pulled her hand out of Umbridge's nape, her fist closed tightly upon what looked to Harry like the edge of a net; albeit one made out of a million exploding stars. What this net could have possibly been, he had no idea— just like he had no idea how a thing of such terrible beauty could have been born of a woman like Umbridge, who was ugly within and without.
Oleandra rose to her feet, raising the shimmering net of golden stars clutched in her fist to around eye-level. She stared into its myriad knots, as if fascinated by its intricacies— but after a few seconds, she slammed the golden net into her breast.
The net exploded into a cloud of minuscule golden particles, which remained suspended in the air for a fraction of a second. Then, one by one, the cloud's particles were each inexorably drawn into Oleandra's body at a rapid pace, giving Harry the impression that he was watching a meteor shower composed of microscopic Golden Snitches.
"What…" Harry said hesitantly, "what did you do to her?"
"The thing she cared about the most was her magic," said Oleandra distantly. "She would only have kept hurting us, so I took her ability to use it away from her."
It boggled Harry's imagination that something like this could be possible— what if he just up and lost his magic one day? Would he have to spend the rest of his life with the Dursleys? Give up on Hogwarts, and learn some kind of Muggle trade? He could not imagine a worse punishment for a Witch, even one as bad as Umbridge…
"Can you do that to just anyone?" Harry asked slightly fearfully.
Oleandra shook her head, her eyes vacant.
"Can't," she said dizzily. "Needed her to follow a very specific ritual for months, for it to work…"
"Then, those rumours about Muggle-Born stealing magic from Wizards…" said Harry hesitantly, "they're not true, are they?"
Oleandra shook her head again; her gaze regaining some of its former sharpness, as her body finished assimilating what she had stolen from Umbridge.
"Technically, I didn't steal Umbridge's magic— that's impossible," Oleandra explained. "I mean, I could have, but since magic is intimately tied to the soul, I would have had to take that instead, like a Dementor. No, what I took were her Magic Circuits— the thing that gives every Wizard their ability to channel the magic around them."
Magic Circuits were sort of like an illusory circulatory system that allowed a Wizard to gather and channel the ambient magic generated by the Wizarding World itself; magic itself being the product of the slow erosion of reality and the laws of order by the primordial sea of chaos in which the World Trees took root.
At any rate, Magic Circuits weren't real organs like blood vessels, but imaginary constructs. As long as a Wizard was alive, they would keep slowly growing thicker and stronger, and even if they were damaged, they would keep repairing themselves ad infinitum.
Under ordinary circumstances, abstract things such as concepts and imaginary constructs couldn't be stolen— but Oleandra was anything but an ordinary Witch.
"Eventually, Umbridge'll regain her ability to manipulate magic," said Oleandra, an impish grin on her face. "But she'll have to start from zero— and since an adults' magic grows at a much slower pace than a child's, she'll be lucky to have reached a toddler's power level by the time she hits her seventies."
Furthermore, Oleandra hadn't just stolen Umbridge's Magic Circuits; she had added them to her own. Meaning that she could now handle much more powerful spells, since she now had a fifteen-year-old's worth of magic, plus a full-grown adult's worth.
But that wasn't all; since a teenager's growth rate is exponential, Oleandra's magic would keep compounding upon itself, so by the time she came of age at 17, she'd be nearly as magical as Dumbledore himself, who was a centenarian…
"What are you doing now?" Harry asked, watching as Oleandra drew her wand and pointed it at Umbridge's forehead.
"Obliviate!"
Oleandra made the universal sign for shush in Harry's direction; erasing memories was the easy part— she now had to implant fake memories into Umbridge's head with the False Memory Spell. Once the Ministry learned that she could steal magic, then a life sentence in Azkaban would probably be awaiting her.
Nothing was more sacred to a Wizard than their magic, after all…
"I think I heard footsteps!" said Harry, urging Oleandra to work faster. "Hurry up!"
Oleandra could hear them too— it sounded like an army was coming up the stairs to the seventh floor. She quickly finished applying her metaphorical plasters to Umbridge's hole-ridden mind, before rifling through Umbridge's pockets. After a cursory search, Oleandra found Harry's wand, which she promptly tossed at him.
"Done!" Oleandra exclaimed. "Harry, we can't let them have the list; Locking Charm, NOW!"
Harry easily snatched his wand out of the air with his excellent reflexes, and both he and Oleandra pointed their wands at the Room of Requirement's door, which was slightly ajar. The other five members of the Inquisitorial Squad were still in there, so they were locking them inside!
"COLLOPORTUS!"