The atmosphere in the arena shifted from loud training to a suffocating silence as **Commander Varkas** pointed his scarred finger at the center of the pit.
"Caelum. Xavia. To the circle," he barked. "Let's see what the Obsidian Wing's 'variable' can do against our new catalyst."
The students backed away, creating a wide ring. **Lyra** and **Seraphina** watched with bated breath, while **Isolde** gripped the stone railing so hard her knuckles turned white.
**Xavia** stepped into the circle, her neon-white hair glowing against her charcoal skin. She didn't use a weapon; she simply stood there, her obsidian Aether leaking from her fingertips like black ink in water.
"Don't hold back, Goldie," she whispered, her voice a low, predatory rasp. "I want to see if that light of yours can actually reach the bottom of my well."
The duel began not with a bang, but with a sudden loss of light. Xavia moved with terrifying, silent speed, her shadows stretching across the floor to swallow Caelum's footing. She struck first, a lash of pure obsidian energy that whistled through the air.
Caelum parried with a solid wall of Gold Aether, the impact sounding like a hammer hitting an anvil. But the shadow didn't bounce off—it *clung*. Xavia's energy began to eat away at his shield, the dark vacuum of her core trying to drain his heat.
"Too slow," Xavia hissed, appearing behind him in a blur of darkness. She delivered a kick that Caelum barely blocked, the force sending a shockwave of shadow through the arena.
For the next several minutes, the class watched in awe. It was a high-speed dance of opposites. Caelum was a sun, radiant and explosive, while Xavia was a void, silent and relentless. She was faster, her body bending and twisting in ways that seemed physically impossible, her black silk robes fluttering like crow's wings. Every time Caelum struck, she vanished into a shadow and reappeared from a different angle, her strikes getting closer and closer to his throat.
Caelum realized that raw power wouldn't win. He needed a different frequency. He closed his eyes for a fraction of a second, tapping into the **Teal Aether** he had synthesized from Lyra during their night in the garden.
"Let's add some velocity to the reaction," Caelum growled.
His aura shifted. The solid gold began to swirl with streaks of vibrant teal. This was **Dual Synthesis**—the ability to use his own catalyst core to trigger a secondary element he had already "collected."
Suddenly, Caelum's movements tripled in speed. He wasn't just moving; he was riding a pressurized gale of golden wind. He met Xavia's next shadow-step head-on. As she emerged from the dark, he wasn't where she expected. He was above her.
He descended like a falling star. He grabbed Xavia's wrists, his Gold and Teal Aether vibrating at a frequency so high it shattered her shadow-cloak instantly. The collision of energies created a blinding flash that forced the students to cover their eyes.
Caelum pinned her to the stone floor, his knees on her shoulders and his hands locking hers above her head. The obsidian energy tried to fight back, but the dual-element pressure was too much. The gold burned through her darkness while the teal wind blew away her anchors.
Xavia lay beneath him, her chest heaving, her neon hair fanned out on the stone. Her obsidian tattoos were glowing a frantic, overheated violet. She wasn't angry; she was looking up at him with a look of pure, shocked exhilaration.
"You... you used her energy," she panted, her eyes wide. "You've already alloyed yourself."
Commander Varkas stepped forward, clapping his massive hands together. The sound broke the trance of the stunned students.
"Jaw-dropping," Varkas admitted, his eyes gleaming with respect. "That is the kind of adaptability that keeps you alive. And you'll need it."
He looked around the arena at the tired, sweating students.
"Class is dismissed! But do not rest! Tomorrow morning, at first light, we depart for the **Wailing Woods**. A field activity to hunt Void-beasts. You will be divided into three-man cells. If you can't synchronize your Aether out there, the forest will bury you."
As the students began to chatter nervously, Caelum helped Xavia up. He could feel the lingering pull of her darkness, but he also saw the way Lyra was looking at him from across the arena—proud, but fiercely jealous of the way he was still holding the shadow-girl's hand.