Ringworld is property of Larry Niven. All characters from the Buffyverse are Property of Joss Whedon. Everything else belongs to me.
The spell kicked in the next day.
While Buffy was taking her makeup exam in ancient history she had a breakthrough. The test question was "Discuss the war strategies used to expand the Assyrian state during the first millennia." At first, she just stared at the paper hoping something would pop into her head. It had never worked before but she kept hope alive. Buffy chewed on her pen and day dreamed as her brain worked on the problem. It took her brain five seconds to recall and organize the information that had laid dormant in her synapses.
"Of course, king Ashurnasirpal II use of inland raids to provide supplies allowed for extended warfare and the expansion of Assyrian forces. That much is obvious. " Buffy smiled to herself. The test became easy almost elementary. Her next makeup test was introduction to calculus. She was well on her way to solving the "Twin Prime Conjecture" and solving one of the oldest unresolved problems in mathematics when the bell rung. She hoped the teacher would give her extra credit.
Willow watched Buffy enter the Magic shop.
She could tell Buffy was happy. She watched Buffy skip her way into the store. Buffy put her books down on the counter and began describing to Giles her success on her makeup exams. Her hands were animated and she did a little dance around the counter. Buffy looked up at Willow with a toothy million dollar smile. Willow could feel her joy from where she sat in the stacks.
"Glad somebody's having a good day." Willow thought to herself. She went back to studying the image on the screen. The ring itself was almost a million miles wide with a surface area of three million Earths. It was spinning with a surface gravity of about one gee. Willow switched to the infrared view. The ring had a regular checkerboard pattern of hot and cold areas almost like a day-night cycle. Someone engineered this thing to be livable. It was not that hard to do the math. There could be trillions of people living there. Trillions!
"What'cha looking at Wil?" Buffy asked. She had sneaked up on her. "Porn? Are you looking at filthy lesbian porn? Not that there's anything wrong with that." Buffy took a peak at the laptop screen.
She saw the ringed star and her breath went out of her. She instantly knew it was an artificial world.
"What the…" Buffy said under her breath. "Wil, can you enhance the area around the star's corona, let's say a million miles out."
Willow tapped the keyboard. Military grade image processing software instantly brought the image of the star into sharp focus. Buffy saw the thin black line that cut across the face of the star.
"Shadow squares." Buffy said. "To recreate the feel of night and day." A terrible idea was forming in her head. 'Wil, where did this come from?"
"Remember the locator spell I did a few days ago? Remember how it split into two sections and one of the sections went towards the sky? I think this is what it was pointing towards."
"It's massive." Buffy said in awe.
"It's mass is equal to the planet Jupiter." Willow added. She looked at Buffy for a moment. "How did you know there would be shadow squares?" she asked.
"Seemed obvious. Once I realized it was built to be inhabited. Because, you know, the ring's distance from the star places it in the green zone, that zone around a star where water can remain in a liquid state. That being the case the diurnal cycle works out to be similar to Earth's." Buffy said without hesitation and somewhat casually.
Willow was staring at her open mouthed.
"When did you become so smart?" Willow asked. She remembered the magic books she had left in their dorm room.
Buff ignored Willow. Her mind was working furiously.
"Willow, tell me about the locator spell you used. The one that went all wonky."
"It was a standard locator spell." Willow responded.
"How do locator spells work?" Buffy asked with urgency in her voice. In the back of her mind, she already had an answer that disturbed her deeply.
"Remember I said I needed something that belonged to Dawn in order for it to work? The spell is basically pattern matching. It takes an object then finds another object that has a connection to it." Willow was trying to understand where Buffy was going with this.
"You used my blood, right?" Buffy asked.
"Right." Willow agreed.
Buffy thought hard for a moment. The monk had told her that Dawn was made from her, that essentially Dawn was a mystic clone of her. The bloodline had split.
"I know what happened." Buffy said with trembling in her voice. This ringworld, it is full of Dawns children, her descendents. There must be hundreds of billions of them there."
"That's not the worst part." Buffy said staring into the Ringworld image. "I've done the math in my head just now. The ringworld is unstable."