Serou's house. The eighteenth month.
Kaito had turned seven.
There had been no celebration. Serou had not mentioned the date, and Kaito himself did not know his exact birthday—Sato used to say only, "Near the end of winter," and leave it at that.
But that morning, Serou brought something different with the two cups.
A page.
"What is that?"
"A diagram," Serou said, placing it between them. "The full seal—or what I know of it. All three layers."
Kaito looked at the drawing.
Complex. Far more complex than anything he had seen before. But now—after eighteen months of reading and study—he could understand part of it.
"This part here." He pointed to the center of the page. "This is what responds to danger."
"Yes."
"And this…" He pointed to one of the outer rings. "This protects the structure."
"Yes."
"But this—" He pointed to the very center. "I've never seen anything like this in any book."
Serou looked at where he was pointing.
"That's because it isn't in any book."
"What is it?"
"That," Serou said slowly, "is the part your mother designed by herself alone." He paused. "The part that has no name."
"What does it do?"
"I don't know," Serou said directly. "That is what I've been trying to understand for five years."
"After all this time—"
"I've understood one thing." Serou looked at him. "That part doesn't respond to external threat. And it doesn't respond directly to the bearer."
"Then what does it respond to?"
Serou paused.
"To the bearer's intent."
Silence.
Kaito said,
"Intent?"
"Not what you decide to do. Not what you think you want." Serou's eyes met his. "The deeper thing. What you truly want in the deepest part of yourself."
He looked at Kaito directly.
"That means the seal wasn't only protecting you from Root that night in Kori."
"But…?"
"It was responding to something inside you when your intent was completely pure." Serou looked back at the diagram. "Your fear for Sato. Your will to survive. Your need to protect."
He looked down at the page.
"Your mother didn't create a protection seal. She created a seal that grows with you."
That sentence stayed with Kaito for an entire week.
A seal that grows with you.
It did not mean power alone. It meant something deeper—that what was inside him was not fixed. It changed. It developed. It responded to the person he was becoming.
And that was the part of Serou's words that frightened him most.
Not Kaito's fear.
Serou's.
Because a seal like that could never be fully predicted.
At the end of the eighteenth month, Serou wrote a single note in his private notebook—the one he showed to no one:
The child is progressing normally.
But the seal is progressing faster than he is.
That difference will not remain small forever.