The morning air inside the Seiki Academy lecture hall was thick with anticipation. Rows of students sat on wooden benches carved with symbols of the ancient Seiki schools, waiting for the lesson to begin. The room itself was alive with subtle energy, walls lined with glowing glyphs pulsing faintly, almost like a heartbeat.
Kaito, Hina, and Riku found seats near the front, the three friends quietly exchanging glances. After the intensity of the Style Trial Combat, this class promised a deeper understanding of what governed their powers—the mysterious and binding Yakusoku: the Vows and Prices that defined the limits and costs of every Seiki user's ability.
Professor Takahashi stepped to the front, a middle-aged man with sharp eyes and a calm demeanor. His Seiki shimmered faintly in a rare blend of Shirabe and Hisui, hinting at a mastery few possessed.
"Welcome," he began, voice resonant and steady. "Today, we delve into the very foundation of our powers—the Yakusoku. Each Seiki user carries a vow, a binding promise that governs their abilities. This is what keeps your Seiki from consuming you, but also what defines the price you pay."
He gestured to the glowing glyphs on the walls, which shifted to display intricate diagrams of Seiki energy flow, interwoven with chains symbolizing vows.
"Without a Yakusoku," Takahashi continued, "your Seiki is unstable, unpredictable, and ultimately dangerous—not only to your enemies but to yourself and those around you. The vow is a double-edged sword: it restricts, but it also grants control and focus."
Kaito's mind immediately flashed to his own vow, the fragile promise he made to protect what little he had left. The hunger of his Void pulsed beneath his skin, a constant reminder that every action had a cost.
"Vows come in many forms," the professor explained. "Some are simple sacrifices: giving up a memory, a physical ability, or a freedom. Others are more complex—emotional bindings, eternal promises, or debts paid in pain or loss."
He paused, letting the weight of his words settle over the students.
"Take Riku's thread manipulation, for example." Takahashi nodded toward the boy beside Kaito, who remained composed as always. "His vow is to never let his threads entangle an innocent—an unspoken rule that limits his range and use. But it also forces him to develop precision and strategy."
Riku gave a faint nod but said nothing.
"Similarly, Hina's blazing fists," the professor said, turning to her. "Her vow demands that she never uses her power to kill. It burns fiercely, but if she breaks that promise, she risks losing her ability entirely."
Hina's eyes flickered with quiet resolve.
Takahashi's gaze settled on Kaito last. "And then there is the Void." His voice softened. "A rare, dangerous Hisui specialization that consumes other Seiki. Your vow is not just a limit—it is a lifeline. Without it, the Void will devour you entirely."
The room grew silent, the air heavy with unspoken understanding.
Kaito clenched his fists, the pulse within him tightening like a noose. "How does one strengthen a vow?" he asked, voice barely above a whisper.
"By conviction," Takahashi replied. "A vow is not just words spoken aloud; it must be believed, felt deeply. The stronger your resolve, the more control you have over your Seiki. But be warned: breaking a vow can have catastrophic consequences. The price can manifest as physical trauma, loss of ability, or worse."
The professor's eyes darkened. "History is littered with those who broke their Yakusoku and paid the ultimate cost."
A murmur rippled through the students.
After the lecture, Kaito lingered in the hall, thoughts swirling. Hina approached, her fiery aura now tempered with curiosity.
"You okay?" she asked softly.
Kaito nodded slowly. "I have to be. My vow is fragile. I feel the Void pulling at me every day."
Hina placed a reassuring hand on his shoulder. "Then we'll make sure you don't face it alone."
Later that evening, Kaito found Riku studying ancient texts in the library, pages filled with diagrams and annotations about Seiki and Yakusoku.
"Riku," Kaito began hesitantly, "how did you make your vow?"
Riku closed the book, gaze steady. "It was simple. I promised myself I would never hurt those who don't deserve it. It restricts me, yes, but it sharpens my focus. The thread is an extension of my will, and the vow ensures it doesn't stray."
Kaito considered this. The idea of a vow shaping power, of discipline born from limits, resonated deeply.
"I want to strengthen my vow," Kaito said firmly. "To keep the Void from consuming me."
Riku nodded. "It won't be easy. You'll need to face the truth of what you're willing to lose."
That night, Kaito lay awake, the shadows in his room alive with restless energy. Memories of his sister flickered—her laughter, her face—and the terrible silence after she disappeared.
He realized the price he was willing to pay was more than a promise; it was a sacrifice of hope, a tether to keep him human.
The journey to mastery was no longer just about power—it was about preserving the fragments of his soul in a world that threatened to erase them.