Panting, Sunlit spun to fire three light spheres in quick succession, tracking just behind Shadestar's erratic path. This was the fifth round in a row, and he couldn't keep going much longer. Shadestar was gaining more and more advantage as the sun sank lower and the shadows lengthened. Her advantage was almost matched by his quickly improving skill, but not quite.
Sunlit felt his eighteenth Sting of the match on his neck. He was getting very tired from the continuous spinning and spell casting. He knew he couldn't keep at this much longer, but he was determined to learn combat magic.
Angrily, he focused through the blurring headache to find Shadestar. His sensor finally found her, and guessing her pattern, he fired behind and to the right of himself.
Shadestar released the shadows again and stepped forward. "Well done, Sunlit. You've improved since this morning."
He smiled through a haze of pain. "Are we finished? I think I've been overexerting my horn today."
Shadestar looked worried. "Sunlit, you know that you won't get a chance to rest in real combat. you have to keep at it and build endurance. Oh, don't look like that. You'll be fine. After round six."
The pale unicorn whirled, only to find the shadows darkened again. He scowled. "No, I'm done for today. I've had enough."
Shadestar's voice floated out from a shadow, along with a painful sting. "Are you now? I think otherwise." she said teasingly.
Rage boiled within him. "I said, ENOUGH!" he shouted, and channeled his rage into his magic. His normally pale yellow aura took on a slight reddish cast as he flung a solid ring of Light spells in every direction.
Suddenly illuminated, Shadestar smiled, and stepped forward. "I was wondering how long I would have to run you ragged before you realized that."
"What? I... I'm too tired...what just happened?" asked Sunlit, his fury forgotten in the wake of a splitting exhaustion headache. Out of nowhere, he had gone from tired to completely exhausted.
Shadestar grinned. "In real combat, you won't have the luxury of playing by the rules. While I did teach you to rely on your magical senses, that comes naturally to any unicorn with a little practice. The real goal was to goad you into breaking the rules to succeed."
Sunlit smiled at this, but then frowned. Tired as he was, that last spell had proved far more taxing than it should have been. He was having trouble staying on his hooves, and the tower seemed to be swaying under him. "Shadestar, why am I this tired? And why did my last spell turn reddish?"
Shadestar, who had been walking to the trapdoor, stopped cold. She turned around slowly and calmly asked "Sunlit, were you focusing your magic through your emotions when you cast that?"
Confused, Sunlit thought hard to pierce the veil of pain obscuring his thoughts. "I...yes, I was angry that you wouldn't stop. I was really angry at the shadows, though. I just wanted them to go away so you'd stop pushing me so hard."
Shadestar looked at him, suddenly very serious. "You should be glad you vented at the shadow rather than at me. I think you had the smallest instant of contact with a Nexus, one of the six sources of magic. I think you touched the Rage Nexus. If you had focused it against me, I might have been seriously injured. More interestingly, when you linked you used a relatively weak emotional force, and even weaker magic. Even the most powerful unicorns in Equestria rarely ever link to a Nexus, and even then only in the most powerfully emotional times. How did you do that?"
Sunlit looked confused. "i don't really know. I just cast my magic like I always do. I drew the magic from my core, channeled it through my mind, focused it with my emotions, and shaped it with my horn." He recited this pattern like a well-known mantra.
The black unicorn's jaw dropped. "Wait, are you saying that you always lens your magic with your emotions? Most unicorns use their logical minds to focus, where did you learn that?"
He shrugged. "I grew up with earth pony parents. I had to teach magic to myself, mostly, and this just came to me. I've always used magic this way."
Shadestar was awed. "But that means...you might be able to access the Nexuses far more easily than any other pony. You could wield tremendous power!"
Sunlit staggered. "Right now, all I want is a soft bed. If Nexus links are this taxing, I'm not sure I want to use them."
His silver maned cousin smiled knowingly. "I'm impressed by your stamina. I expected you to try to give up after round three. Believe it or not, I've been fighting fatigue a bit too. Come on, there's a couch you can have."
Sunlit was only too happy to follow. Falling down the stairs once or twice was worth the effort as he drifted off a few minutes later.
Shadestar, however, was not asleep. She was used to staying up for more than 48 hours straight chasing a new rune to perfect a ritual circle, or finding a new nuance of a spell. She quietly crept to the spire's basement and her enchanting and alchemy laboratory.
She approached the circle in the center of the room, fifteen hooves across with a pentagram in the center of its ornate carvings.
Sitting down in its center, she relaxed her mind, focused, and looked into the aura of her sleeping cousin. Her scry was well hidden, to make sure not to wake him. As she puzzled over his magical center's intricacies, she found something - or rather a lack of something - that stunned her.
"He has no natural limit," she said quietly to herself. "He can link to Nexuses as often as he wants, and he's so practiced at emotional lensing, he could channel power to overcome all the princesses at once."
After a moment, Shadestar smiled. "Well, at least he has a strong and moral heart; combine that with how rarely he allows himself to really get angry, and Equestria should have nothing to fear from him." Her thoughts darkened as they turned to the few other ponies who had ever been like Sunlit. "For now."
Deciding her worry worth acting on, Shadestar channeled magic through herself and the circle, activating one rune carved into the far wall. She could not keep Sunlit's potential a secret from the ones who had the most to fear from it.
As a chill wind swept around her and a deep blue glow suffused the room, Shadestar hoped she was making the right choice.