The ' tree', which they though was a tree, was merely an illusion. Underneath it, was a cave.

" It's dark in here." Mia echoed, looking around the dense yet strangely dry cave. It was illuminated by different types of crystals and geodes, and both Nelson and Mia, who liked free souvenirs from their adventures, broke off chunks of the rocks and crystals and stored them in the bag Nelson was carrying. 

" Wouldn't it be funny if all this is just a setup from Wu?" Nelson laughed freely. Mia, though, had a troubled expression on her face.

" But for a year? Surely, if he was okay, we wouldn't need to use that blob back there to talk to him. Speaking of which, where is it?" Mia, Blackie, and even Nelson, who looked away from the crystals long enough to scan the cave, turned everywhere to find something, anything- a yellow light, some ghost that looked like Wu, ANYTHING. They didn't want to admit it, but, they were getting desperate.

The cave stretched on and on, a labyrinth carved from the heart of the mountain. The air hung heavy with an unsettling stillness, broken only by the rhythmic drip of unseen water and the occasional chirp of an unseen creature. The dazzling clusters of crystals that had initially lined the entrance had dwindled, replaced by an oppressive darkness.

"It's getting colder too," Nelson muttered, pulling his jacket tighter around him. He glanced at Mia, her face illuminated by the faint glow of her new camera screen.

"Mia? You alright?" he asked, his voice laced with concern.

Mia didn't answer, her brow furrowed as she scrolled through the photos she'd taken of the crystals. A faint, nagging unease gnawed at her. Everything about this cave felt wrong. The unnatural silence, the strange warmth that lingered despite the growing cold, the sudden lack of crystals – it was like the cave itself was actively trying to hide something.

"Blackie," she called out softly, her voice barely a whisper.

The ever-attentive cat materialized at her side, his emerald eyes gleaming faintly in the darkness. He let out a low growl, his fur bristling on his back.

Mia glanced at Nelson, who was staring intently down a side passage that branched off from the main tunnel.

"Did you hear something?" she asked, her voice barely above a whisper.

Nelson hesitated, then shook his head. "No, but... this passage seems different. Maybe it's a shortcut?"

Mia's instincts screamed at her to stay put, to retrace their steps and find their way back to the comforting sunlight. But the thought of Wu being trapped somewhere in this cave, and the flicker of hope Nelson's words ignited, spurred her forward.

With a deep breath, she grabbed Nelson's hand, her touch warm and reassuring in the oppressive darkness. "Let's check it out, but be careful," she warned, her voice firm despite the tremor running through her.

Together, they ventured down the side passage, Blackie padding cautiously at their heels. The air turned stale and heavy, and the darkness seemed to solidify, pressing in on them from all sides. The silence was deafening, broken only by the soft crunch of their footsteps on the rocky ground.

Suddenly, a flicker of light pierced the darkness, casting an eerie glow further down the passage. Mia's heart hammered in her chest. Could it be...?

With a newfound urgency, they hurried forward, their steps echoing in the oppressive silence. As they rounded a bend, the light source came into full view.

And the sight that greeted them left them speechless.

 It was the orb.

The glowing orb pulsed with an ethereal light, casting long, distorted shadows on the cavern walls. As their eyes adjusted, Mia and Nelson gasped in unison. Suspended within the orb, his wizened face etched with concern, was Master Wu.

"Mia?! Nelson?!" his voice boomed, echoing through the cavern. "Didn't I tell you not to come here? It's too dangerous!"

Shame washed over Mia. "Sorry, Master," she stammered. "We were just worried. We used Dove to try and find you, but..."

Wu sighed, the sound heavy with weariness. "I understand your concern, young ones. You have a right to be worried."

Hope flickered in Mia's eyes. "Master Wu, where are you located? Is there a way back?"

Wu's spectral form flickered slightly. "I am trapped near a waterfall," he explained. "The journey there is fraught with peril. Ancient booby traps, treacherous terrain, and... well, let's just say you won't be alone."

Nelson, ever the optimist, grinned. "Sounds like an adventure! As long as we're together, right Mia?"

Mia returned his smile, a newfound determination hardening her gaze. "Right, Nelson. We can do this. Master Wu, did you say working together will make it easier?"

A hint of a smile played on Wu's spectral lips. "Indeed, my students. Teamwork is the key to overcoming any obstacle. Remember, your strengths complement each other. Now, prepare yourselves. The path to the waterfall is long and arduous, but with courage and cooperation, you will find me."

The orb pulsed once more, then faded, leaving them in an inky blackness. The oppressive silence returned, broken only by the ragged sound of their own breathing.

"Well," Nelson said, his voice tinged with nervous excitement, "looks like we have a waterfall to find. Ready for an adventure, Mia?"

Mia squeezed his hand, her voice firm. "Ready as I'll ever be."

Together, they stepped forward into the darkness, the echo of Wu's words ringing in their ears. The journey ahead would be tough, but with their combined skills and unwavering determination, they were prepared to face whatever dangers awaited. They were ninjas, after all, and nothing would stop them from reaching their master.