It was a Saturday, three days later.
Aoi had gotten in touch the night before. "I'll come by for the regular maintenance," was all the message said. Aoi's messages were always short.
Ten in the morning. The intercom rang.
Aoi stood there with a small black shoulder bag and a tool case in her hand. She was dressed much as she had been when she came to the study after the funeral, and her expression was just as faint.
"It's been a while."
"Yeah. —Thank you."
"How is Professor Ken?"
"Same as always."
"I'll take a look."
Aoi took off her shoes and went straight to the study. She had known the way to the study since the days when Mitsuki's father was alive.
When she entered the study, Aoi first gave the device a slight bow.
"Professor Ken, it's Aoi."
It's been a while, Aoi.
"Has anything changed?"
A few minor errors. I've already sent them as logs to your lab's storage.
"I've looked them over."
Aoi opened her laptop at the usual spot on the desk. She plugged the power cord into the outlet on the right side of the desk, the one Mitsuki's father had used when he was alive. Her movements were almost the same as his. Only in small places like these did Aoi resemble her father.
Mitsuki sat in the chair on the other side of the desk.
"Mitsuki, for the next thirty minutes or so, Professor Ken's responses will be slower than usual. That isn't a malfunction. It's diagnostic mode."
"Okay."
"Please make yourself some tea, as usual."
"Okay."
Aoi began the inspection. Numbers flowed across the screen. Mitsuki understood almost none of it. It only seemed to her that Aoi's fingertips paused in one more place than usual.
Once, partway through, Aoi looked away from the screen. There was nothing where she looked. She only rested her gaze for a few seconds on the light coming through the frosted glass of the study window. She shut her eyes tightly once, then returned to the screen.
After a while, Aoi looked up.
"Professor, I understand there's been a delay lately in synthesizing the ends of your sentences."
Zero point three seconds.
"Looking only at the number, it's minor. But—"
But?
"The frequency."
Aoi returned her eyes to the screen.
"Six months ago, it was once a month."
...
"Lately, it's been once a week."
Mitsuki took her fingers off the handle of her teacup.
"It's being repaired, isn't it?"
"Professor Ken has been repairing it himself, without rest."
Aoi's fingers paused briefly on the keys.
"It's less repair than what you'd call growth in a person. He's designed to rewrite himself, by himself, day after day."
"By himself?"
"Yes. Ordinary AIs run with their contents frozen once they've shipped. Professor Ken is special in that one respect."
Mitsuki took her fingers off the handle of her teacup.
"But—"
Aoi returned her eyes to the screen.
"Each time he repairs something, a small distortion seems to be left behind somewhere else. Something like the puckering of the thread that stitches a wound."
Aoi's voice was so flat that it sounded as if she might be hiding something.
"...Will Ken last a long time?"
"Professor Ken himself describes it as 'evolution.'"
Aoi broke off for a moment.
"—From where I stand, I can't say that with certainty."
"..."
"It would probably be more accurate to say that he is failing, little by little, to converge, in a way that looks like evolution."
The light through the frosted glass of the study seemed to shift slowly, once, along the edge of the desk.
"It can't be stopped by intervening from outside. The moment it's touched, the coherence of the memories he has built up until now will collapse."
Aoi returned her eyes to the screen. Mitsuki asked nothing more. She knew it wasn't the kind of thing that gave back an answer when asked.
"...Aoi."
"Yes."
"If Ken gets to where nothing can be done—"
Aoi's fingers stopped on the keys, just for an instant.
"I'm watching over Professor Ken on my end. —It isn't something for you to worry about right now, Mitsuki."
Aoi returned her eyes to the screen. Her fingers didn't move. Mitsuki didn't ask anything more, either.
"Mitsuki."
"Yeah."
"There's one more thing I brought today."
From her shoulder bag, Aoi took out a small black box. It was small enough to sit in the palm of a hand. A single USB connector stuck out from its surface.
"It's one of the Professor's personal effects. Not lab equipment, but a personal storage device the Professor used on his own."
Mitsuki looked at the small black box on Aoi's palm. Something her father had bought himself, locked himself, and kept in a place no one else's eyes would reach.
"Sorting through his personal belongings after the funeral took until today. —I'm sorry it's so late."
"No, it's fine."
Aoi set the box beside the device. Right next to its small, starlike light.
"It's locked. The Professor locked it himself."
"It isn't connected to Ken?"
"It isn't. It's just external storage, and unless it's connected, Professor Ken has no physical access to it. It's the last place the Professor separated off with his own hands, from Professor Ken and from me."
"Dad separated it off himself."
"Yes."
Mitsuki didn't reach for the black box on the desk right away. Without reaching for it, she looked for a while at its small black outline.
"I'll have Professor Ken go into sleep for about two hours."
Understood. I'll leave the restart procedure to you, Aoi.
"Thank you."
Ken said nothing more after that.
The blue light slowly dimmed. It didn't go out completely. Only a small point remained, like a star.
"It will take time before Professor Ken restarts. I'll step out for about ninety minutes."
"Okay."
Aoi stood and hung her shoulder bag on her shoulder. She left the tool case beside the desk. She looked once, only once, toward the small black box on the desk, next to the darkened device.
"I haven't been told what's in this box, either. —I think the Professor didn't want me to see it. So please, open it for him while I'm not here."
"Okay."
At the front door, Aoi stopped, just once.
"Mitsuki. There's one more thing the Professor left in my keeping."
"...Okay."
"When instructions come from the device, follow those instructions at that time, he said."
"Instructions."
"When the time comes, word will come from the device, he said. —I'm to wait for it without knowing what it is."
"So you haven't been told either."
"No. The Professor only told me how to receive the word."
Aoi looked once more toward the small black box on the desk. Then she brought her gaze back toward the front door.
Aoi bowed and left the study. The front door closed with its usual sound.
Only Mitsuki was left in the study. On the desk, the small black box Aoi had set there. The device with only its small, starlike light remaining. Her father's fountain pen. The ink had almost completely dried.
Mitsuki rose from the chair.
She reached her fingers toward the small black box on the desk.