Chapter 27: A Binding Vow
Honestly—this so-called Construction Technique was garbage.
Ren's own Limitless Probability Technique might have low efficiency, but at least every activation carried the potential to overturn the battlefield. Each use had weight.
But this technique? One bullet per day. Two bullets, and you collapse.
Was it meant for killing enemies—or committing suicide?
He had thought it was a trash technique from the beginning. Out of respect for his classmate, he had never said it out loud.
But this time it had nearly cost Zen'in Mai her life.
He couldn't stay silent.
Mai didn't respond immediately. Only after a moment did Ren realize the sound of chewing had stopped.
He turned to look at her.
Her face was filled with something complicated—anger, hurt, stubbornness, pride.
After a long silence, she fixed her gaze on him, cheeks puffed out with apple still in her mouth.
"My business is none of yours!"
He instantly realized he'd stepped on a landmine.
This wasn't the time to force logic on her.
He didn't argue. He simply waited. When she finally swallowed the apple in a huff and he offered her another slice, he asked quietly:
"Is there a reason you have to use that technique?"
"I'm a jujutsu sorcerer!" she snapped. "What kind of sorcerer doesn't use her innate technique?"
Then she froze, suddenly aware of what she'd said. She immediately turned her head toward Miwa.
"Sorry! Miwa, I didn't mean—"
"I-it's fine!" Miwa nodded quickly, like a pecking chick. "I know you didn't mean it."
"So that's it?" Ren asked patiently.
"I told you to drop it!" Mai shot him another glare, then glanced at Miwa again.
He chose his words carefully.
"Honestly… your technique isn't really stronger than Miwa having none."
Mai's jaw tightened.
"I think," he continued, "instead of pouring everything into a technique that hurts you, you'd benefit more from refining your cursed energy control—like Miwa does."
"No." She bit down hard on the word.
After a pause, she added reluctantly:
"There's someone I have to catch up to. Someone I have to surpass."
"If I don't use my technique… it'll be impossible."
Ren studied her face. The irritation had faded. What remained was iron resolve.
He sighed softly.
If he were honest—even to himself—he didn't just want her to abandon Construction Technique.
Part of him wanted her to abandon the life of a sorcerer altogether.
Her innate technique wasn't just weak—it bordered on self-destructive.
And her personality… proud, competitive, easily provoked.
In the jujutsu world—a profession where one mistake meant death—that was dangerous.
Miwa was different. She was meticulous. Hardworking. Careful. Those traits compensated for her lack of an innate technique. And her family relied on the salary—she had no real choice.
But Mai?
She wasn't trapped.
She chose this path.
And she was choosing to burn herself alive to walk it.
Ren lowered his eyes, the apple knife still in his hand.
If she insisted on walking forward—
Then maybe the answer wasn't stopping her.
Maybe it was changing the rules of the road.
But seeing the look on her face, Ren knew no amount of persuasion would work.
Still, he couldn't just stand by and watch this reckless, overly proud—yet frighteningly fragile—girl one day meet disaster.
If he couldn't stop her…
Then he would have to change something else.
---
A few days later, Zen'in Mai was discharged from the hospital.
After thanking the classmates who had come to see her, she was suddenly dragged into a corner of the classroom by Ren, who claimed he had prepared a "discharge gift" for her.
"This guy… that impatient?" she thought, watching him hurry over with an excited grin.
Come to think of it, it had been a while. Lying in the hospital bed for days had nearly rusted her bones. A little "intense exercise" wouldn't hurt.
"I've been thinking about your situation for a long time," Ren said gravely.
Thinking for a long time?
Mai's mind went blank.
Thinking about what, exactly?
Don't tell me this idiot is actually some kind of pure-hearted romantic? She almost laughed. Is he about to say he'll take responsibility for me or something?
Wait.
He wouldn't suddenly pull out a ring and kneel down, would he?
For the first time in days, Zen'in Mai felt genuinely flustered.
"Let's make a binding vow," Ren declared solemnly.
"Wh—what? A binding… vow?"
Her eyes widened.
Binding vow?
That kind of binding?
Her thoughts derailed at once—contracts, restraints, master–servant agreements… even a flash of leather straps and dripping candle wax passed through her mind.
"Yes. A binding vow," he repeated firmly.
"B-binding?" she stammered, half thinking that maybe… just maybe… it wasn't entirely unacceptable—while also deciding she should clarify exactly what he meant.
"I've thought it through," he continued, utterly serious.
"Your technique, if you don't optimize its efficiency, is practically unusable."
"Op… opti—"
Wait.
Technique?
Mai's eyes snapped open.
"You're talking about my technique?"
"Of course." He nodded, puzzled by her reaction. "Normal methods have probably already been exhausted, right? Improving cursed energy control, refining execution—you've surely tried everything conventional."
She stared at him, her earlier fantasies evaporating like smoke.
"So the only options left are unconventional ones," he continued. "And I've come up with one. We use a binding vow."
"Wait, so you're not—"
"Not what?"
"N-nothing!" she blurted quickly. "You're saying you can help improve the efficiency of my Construction Technique?"
"Yes." He nodded again, perfectly calm. "After you told me about binding vows and revealing one's technique, I became interested in the mechanism. I've spent the past few days researching in the library—information about binding vows and about Construction Technique itself. I even asked you questions about it earlier, remember?"
"I remember."
Now fully focused, Mai listened intently, eyes locked on him.
"Based on what I've gathered," he said, "I think there's a viable solution."
"Construction creates real matter. It doesn't disappear when the technique ends. Once created, it exists permanently. Correct?"
"Correct." She nodded. That was both its greatest strength—and its fatal flaw. Creating tangible reality required an absurd amount of cursed energy.
"Then we place the binding vow on the created matter itself."
He looked at her steadily.
"In exchange for the matter you create deteriorating at ten thousand times the natural rate…"
"…your cursed energy control precision will increase ten thousandfold."
Silence fell between them.
A binding vow.
Trade permanence for efficiency.
Sacrifice durability—
To gain mastery.
Mai's breath caught.
For the first time, her so-called "trash technique" no longer sounded like a curse.
It sounded like a weapon waiting to be reforged.