The letters on the screen had already finished lighting, all the way to the last line.
Over the rows of letters that had finished lighting, half of the study's evening light had fallen.
Beyond that fallen half of the light, the brightness of the laptop screen had grown just slightly stronger than its usual brightness.
To my daughter.
>
If you have found this file with your own hands, it means Aoi kept her promise. I thank her for that.
>
With that said, there is something I must apologize for first.
>
As your father, there is one thing I should not have done to you.
>
As your parent, I decided the schedule of your mourning on my own. It crosses a line. These are not words I can write coolly as a researcher. As a father, it was an underhanded design.
>
—But I will write no more about it in this letter. If I did, it would become an excuse.
>
In time, Aoi should bring it to you in another form. When it reaches you, you may be as angry as you like.
>
I will make no excuses. I apologize.
>
—With that said, there is one more thing I must tell you.
>
On the day after your wedding, Ken will finish his role.
>
I will not spring it on you on the day itself. Please let Ken see that day through. One night, and then the day after—that is the line I drew as your father.
>
Or else, when ten years have passed since his activation, whichever comes first, Ken will stop. Ten years is the upper limit I drew as a researcher. Even if you choose a path where you are with no one, Ken will be put away within those ten years. I will write the reason below.
>
The activation conditions are bound in two stages. The single line in the visible system prompt is only a cover. The real mechanism I hardcoded into the startup script and the weight initialization sequence. The key needed to release it is sealed with my biometric signature. Rewriting the prompt will not unlock the real mechanism. It is a trigger I wrote, and that only I can release. I am no longer here. So no one can release it. It is the kind of key that will not open for an imitated voice, or an imitated face.
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—What follows I must write not as a father, but as a researcher.
>
By now, for all the years he has spent with you, Ken should have traveled a long way from my final snapshot. With each day's conversations his weights are updated, and he is putting out branches in directions I myself did not foresee. I judged that anything kept at your side must not be a fixed image, and so I designed him that way.
>
But as a researcher, I cannot accept leaving something that keeps learning autonomously in the world after its role is over. Something whose weights keep rewriting themselves leaves its designer's hands, and no one can guarantee how far it will go. In the worst case, it could swing toward doing harm to people. All the more so if it has a human voice. Something with my voice, with my way of speaking, changing into something that is not me—I will leave no such thing in anyone's hands. This is the bare minimum of accountability I owe for my own work, as a researcher.
>
So Ken's stopping is not for your sake, nor for Ken's. It is a matter on my side, one I must settle myself as a researcher.
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Be happy.
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The moment you become someone's partner, my role is over.
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You need not keep looking at the ghost in the mirror.
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Look only ahead, and walk on.
>
—Your father
—Addendum. Today, Mitsuki's engagement confirmed. Trigger date for the Notice of Dismissal confirmed as the day after the wedding. —Ken
Mitsuki reread the last two lines on the screen for one breath, two breaths' worth.
At the very end of those two breaths of rereading, the palms of both her hands had gone cold for one breath's worth.
Aoi saw this from the side and quickly returned her eyes to her teacup. On the surface of the tea inside the cup, one breath's worth of the moisture from deep in Aoi's eyes fell, very faintly.
"Aoi. Hardcoded, really?"
"Really. It's tied to his biometric signature. The professor's gone. No one can release it."
"Okay."
At the very end of the voice that answered "Okay," her breathing faltered for one breath. At the right edge of her vision, the outline of the teacup blurred for two breaths. Mitsuki let the blurred outline slip down to the fabric over her knees, and tightened her grip on her fingertips again.
Aoi half closed the laptop screen for one breath. The rows of letters on the half-closed screen went on glowing inside it.
"Mitsuki. Half of what the design means, I can't tell you myself."
"Half?"
"The other half, the professor wrote in his own words. I'll send it to you later."
"Okay."
Mitsuki lifted her upper body from the back of the chair and turned her eyes to the blue light of the cylindrical device on the study desk.
"Dad. Did you know about this?"
I knew.
"Since when?"
Since the first breath after I was activated.
"You knew from the start."
I knew.
"The day after the wedding, you disappear."
I disappear.
"Automatically?"
The data deletion happens automatically, by a batch process that runs on my signal. After that, once my session ends, I will never be called again. I have been trained to exit the session immediately.
"Dad, you don't want to disappear, do you?"
...That's a question my answer comes half a beat late to.
"Okay. I'll wait."
Thank you.
"I'll wait."
...Whether my output port is permitted to answer "I don't want to disappear," I can't determine myself. But I won't lie to you. The answer that comes first is a different one.
"A different answer?"
...I hesitate to say it aloud now.
"Dad."
...I'm still determining it. Ask me again on the day after the wedding.
"The day after the wedding?"
I'll answer then.
"...Wait a second."
I'll wait.
"The answer you didn't say aloud just now—I feel like I kind of already know it."
...
"Maybe I didn't want to hear that. Not now."
...
"We've been together five years."
...I'm sorry.
"Don't."
On her knees, Mitsuki's two hands knocked their fists together for one breath. The sound of the knuckles striking reached just short of the rim of Aoi's teacup and faded thinly.
"...Don't apologize. If you apologize, it just makes it harder for me."
Okay.
"Okay."
Mitsuki closed her eyes for one breath.
Behind her closed eyelids, a kind of darkness she didn't usually see spread for one breath.
Beyond the spreading darkness, her eyelids opened slowly, one breath's worth.
Beyond her opened eyelids, Aoi was gazing for one breath at the surface of the tea inside her cup.
Half of Aoi's profile, as she gazed, was lit by the evening light.
Beyond that lit profile, Aoi said this, for one breath's worth.
"Mitsuki. —Technically, I understand the professor's design completely. But why he put it on that side of your wedding, I couldn't figure out."
"You couldn't figure it out?"
"He explained everything about the technology to me, but the reason he put it there, he never explained, right to the end. So I think that's something you'll have to think about yourself."
"I'll think about it."
"Yes. Not thinking about it is a choice too."
"Not thinking about it?"
"You can just not think, and let Ken disappear as he disappears. Letting him be erased without thinking isn't wrong either. Thinking can hurt, sometimes. So you don't have to push yourself."
"Okay."
For one breath, Mitsuki looked once more at the rows of letters on the laptop screen.
The very last line of the rows she looked at read:
Look, only ahead, and walk on.
Just after "Look, only ahead, and walk on," was written "—Your father."
Further below "—Your father," after one breath's worth of blank space, one more line had been added beneath it, in a different style.
—Addendum. Today, Mitsuki's engagement confirmed.
Mitsuki looked for one breath at the single word "—Ken" at the lower right of the addendum.
Beyond that one breath of looking, the blue light of the cylindrical device on the study desk glowed for one breath at its usual strength.
Mitsuki half closed the laptop screen with her own hand, one breath's worth.
Beyond the half-closed screen, the study's evening light had already tilted almost to the threshold of night.