While we wait, here's more Grimdark Rachel being Grimdark (although your mileage may vary applies).
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Rachel pulled out the cables closer, until the sparks from the exposed copper wire illuminated. The tree-thing's panic peaked, gasping and hyperventilating and trying to squirm out of the enraged operative's grasp.
"I didn't always fly a desk," Rachel said wistfully, ignoring the plant's plight, "I used to be in Intelligence. In field operations. Infiltration, sabotage... All that secret, backstabby stuff. "Heartbreaker", they called me," she recalled fondly, "But you know that, right?"
"Yes!" the tree squeaked, "We... W-we have you on file. Y-your record..." His eyes lit up with a faint glimmer of hope. "D-did you k-know, t-ha... that you were in the list of candidates?"
Rachel raised an eyebrow by a millimetre, and the wires drifted away. "... Really?" she asked, sounding curious.
"Y-yes!" she alien said, nodding feverishly, "Y-you and Numbuh 274- I mean Chad! You were both the top of your class, above and beyond the other operatives in the Kids Next Door! You know the reputation Chad had... great leader, excellent operative, c-charismatic, unbeatable in the training ring... And you! Director of Intelligence, spotless record, great strategist and planner-"
"And yet," Rachel interrupted, "Here we are. How strange."
The tree gulped. "N-numbuh One rose up in prominence after Chad, uh, pretended to defect. A-and you... I don't know!" it cried, "N-nuh-Numbuh Infinity w-was the one who v-vetoed your application before w-we had a chance to t-tell you! H-he f-ound something when he was digging through your files, something about a Sector that doesn't exist-"
"You mean Sector S?" Rachel asked. At the tree's nod, she chuckled darkly. "Oh, it exists. And I can see why he wouldn't want me to be part of your little club if that's what he found."
"A-and what would that be?" the tree asked.
"I don't remember!" Rachel said, cheerfully, "Really, I don't. Partial Decomissioning is a thing when you're working with that level of secrecy; Numbuh Infinity probably knows more about what I did than I do."
For some reason, Rachel found this to be hilarious. She giggled, and then brought the sparkling cables closer.
"Aha!" she cried, "You were trying to distract me!" She grinned. "Clever little tree, you ought to ask for a medal. If there's enough of you left afterwards. But as I was saying; I was in Intelligence once. And there's a really, really simple way to test how dedicated an operative is to the cause: pain."
She held the sparking wires between her and the tree, the light from the arcing electrical current giving her face an almost demonic appearance.
"Resisting torture was a key part of my training at Spy School," she explained, slowly bringing the wires closer to the tree's leaves, "After all, an infiltrator who blabs at the suggestion of merely being force-fed asparagus is a really cruddy infiltrator, and there are worse things out there that they can threaten you with.
"And sure, there are ways to train yourself to resist pain and suffering," she continued, "To make it seem... less than what it really is. But at the end of the day, it all boils down to a very simple question: How much pain is your loyalty worth? Is it worth eating through a wall of broccoli? Is it worth a month in a cell with no sun and little food? Or, more to the point, is it worth being set on fire?"
The tree thing gibbered. It sounded like it was begging for mercy.
Rachel ignored it.
The wires brushed the leaves. It took a while for the fire to get started, the tree wailing and flailing the whole time. Rachel didn't mind the hits, she could take the pain.
"There are two fire extinguishers nearby," Rachel said, quickly and loudly enough to get the tree's attention, "One of them is in the elevator right behind me. The other's past that door, down a long, long corridor. Go for the one deeper inside -passcode's 1-9-1-5, by the way- and you can lock the door behind you; stopping me from going further in and foiling my plans. But, to do that, you'll have to go though a pain you can't even begin to imagine. You might not even make it to the extinguisher, even!"
"Go for the one in the elevator, you'll just have to go through a little bit of pain. Bu if you do, I'll lock the door, send you up, and collapse the shaft, making it very hard for any of your buddies to get down here and stop me."
She abruptly let go of the tree, and took two steps back.
"So," she said, opening her arms, "What's it gonna be, Numbuh 74.239?"