There are two kinds of things we do not know.

One is something we do not know the answer to.

The other is something we do not even know we do not know.

Put that way, the second kind of unknown sounds far more remote, but it is surprisingly close at hand.

Look back through your memories. Think back to your sparkling childhood, long ago, and you are sure to find some radiant memory that made you special.

Back then, you were the center of the world, the master of the grandest dreams, the hero of a magnificent epic.

Yet the little things buried within those shining memories never come to light.

Things that were not special at all. The chill of a glass of water you drank one morning, or the warm, nutty smell of a pillowcase steeped in sunlight—things that brought color to your days yet are so very hard to remember sink beneath the surface, never to rise again.

You cannot even try to recall them until someone mentions them. And even if you do bring something to mind, it is not a memory of that day. It is merely an imagining pieced together from everything you have experienced since.

Memory is an abyss that unassuming, and that unfeeling.

So surely no one could blame me.

Not even if I failed to remember something no one had pointed out.

"Wait. Shei."

"Huh?"

"Aren't we forgetting something?"

The Regressor scowled fiercely and retorted,

"That again? Can't you just say what you mean?"

"What again? What are you talking about?"

"That goddamn way you talk! You replace the subject, verb, and object with 'something' and just ask questions!"

Stung, I hastily waved my hands in denial.

"That's unfair. I really can't remember either! This time, at least!"

"So you do know you do it, you bastard."

What an undeserved dressing-down. Devastating as it was, this was no time to dwell on such trifles.

The bundle the officer had received from 'them.' The one she had been told to open when she needed a helper. Inside, along with a broad, fan-shaped leaf, was a message: [Recall the forgotten being].

The officer still hadn't remembered, but the problem was that I, too, had forgotten who this forgotten being was. Mind reader or not, I couldn't recall something when I didn't even know what it was.

But there had been something. Something fairly important that had slipped my mind.

I strained to bring that hazy memory back.

"What was it? It had something to do with you. Shei, could you describe your defining traits?"

"What the hell is wrong with you?"

"It's urgent. Hurry."

At my insistence, the Regressor crossed her arms and pondered.

"My defining traits...?"

'Regression... Can't mention that. Devourer of Fortuitous Encounters, master of a treasure vault. Carried by my gear... Tch. Why is this the only crap coming to mind?'

An honest self-assessment, at least. But that wasn't what I wanted to know.

Struggling, I began listing the Regressor's traits one by one.

"Distrusts people, likes men. Prickly, runs a one-armed-man factory..."

"Do you want to die? Why is that the crap you're coming up with?"

"One-armed-man factory? One-armed-man factory. Right-arm killer. Got it. The right arm!"

"Seriously? That's it? You're making fun of me, aren't you?"

Making fun of her? Did she think I was the sort to mock people for no reason?

I wanted to give her a piece of my mind, but this wasn't the time. I whipped around to face her and shouted,

"The right arm! Where's the right arm?!"

The Regressor's face twisted into a scowl.

"On your right. Why, should I cut it off and show you?"

"This isn't the time for wordplay! Rash, the undying one! His right arm! Where is it?"

"... The undying one?"

Only then did the Regressor realize what I was looking for and dredge up the undying one from a corner of her memory.

The right arm rotting under a curse, the flesh scattered in pieces, and how she had made a healing potion to lift the curse and submerged his right arm in it.

But nowhere in her memories was there any recollection of taking the healed arm back out.

Of course there wasn't. She had put the arm in the healing potion and completely forgotten about it!

The Regressor sighed.

"Oh. I forgot."

"Forgot? How could you forget that?!"

As I shouted in disbelief, the Regressor fiddled with her hair, looking flustered herself, and offered a meek reply.

"W-well. I put it in the healing potion to treat it, you see. When a right arm keeps flopping around like that, you kind of want to forget it."

"That's quite a talent! Doesn't that arm walk over on two fingers and smack you when something annoys it? How do you forget that?"

"Well, it kept trying to climb out of the tank of healing potion before the curse was lifted, so..."

"So?"

The way only her eyes shifted reminded me of Azi playing innocent after causing trouble. What on earth had she done?

"I chained it up and sank it."

"Sank it?"

Even I hadn't done that. When it came to heavy-handed behavior, she would resent taking second place to anyone.

"Well, fine. Let's say that was understandable. But you must have seen it while passing by!"

"Well, the thing is, the healing potion smelled so strong that I put it in an out-of-the-way room. And set up a barrier around the room so the smell wouldn't get out..."

"Excuse me, are you sure you're lifting a curse? That's just a sealing spell, isn't it?"

Unbelievable. I thought I lived a fairly unplanned life, but the Regressor was the sort who threw away even the plans she did have.

During the three days I spent reviving Tyr's heart, the Regressor had become so curious about what was happening that she had abandoned the undying one and forgotten him entirely!

I gave her an icy look.

"... Shei. Do you dislike Rash, by any chance?"

"Uh, honestly, I'm not all that fond of him."

"Hmm. So liking men doesn't mean you don't have standards."

"Stop harping on that crap! I just forgot, that's all!"

'I did lock it away too far out of sight... Just seeing that flailing right arm brought back visions of that horrible corpse golem. After that, I was too busy with Tyrkanzyaka's heart to spare it any attention... I need to reflect on this. I was too narrow-minded.'

So she did reflect on her actions. Apparently she still had a human heart left in her.

Well, what did it matter? People forgot things sometimes. Certainly not that I was saying that because I'd forgotten too...

"Wait! More importantly, you were the one using his arm! You should have remembered it too!"

... I took it back. This moral degenerate didn't even know the meaning of remorse.

Of course, I had forgotten too. As the owner of the Immortal Right Arm, I acknowledged a very small share of the responsibility.

But still.

"My circumstances were different from yours."

"What excuse are you going to make? We both forgot, didn't we?"

"I nearly died trying to revive Tyr's heart, unable to remember even who I was. You expected me to remember some swarthy man's right arm in the middle of that?"

"... Well."

"I even left a note, taking the possibility of memory loss into account. What about you, Shei, with all your faculties intact?"

"..."

"If you have something to say, let's hear it. I think we need to weigh your conscience today, Shei. I suspect it'll weigh about as much as Sky Cherry Blossom."

Even with ten mouths, she would have had no defense.

The Regressor crossed her arms and put on an unnecessarily dignified air, then casually turned and pointed outside. She was dodging the question.

"I sealed the right arm in the convict laborers' quarters over in that corner. Well, it's nothing urgent, right?"

"We're very late already, but let's go."

I headed in the direction she indicated.

Dozens of indistinguishable doors lined the corridor of the convict laborers' quarters. Some were broken, others torn off altogether, but even that vandalism did little to distinguish them. Signs of violence were everywhere. Anything hidden here would be hard for anyone short of Azi to find.

"This way."

The Regressor opened the door to a room at the far end. The moment I stepped inside, a wave of heat washed over me.

The pungent scent of herbs stung my nose. Beyond the hazy fumes filling the room, I could see a rectangular tank sitting on the bed. I felt my way forward and looked inside.

Inside the rectangular tank were a clear, bubbling healing potion and the undying one's right arm, chained up and sunk to the bottom. It looked for all the world like some ancient ritual.

I turned silently to the Regressor. She averted her eyes, apparently unable to defend herself.

Pointing at the tank, I asked,

"You've left it like this all this time?"

"... Yeah. All I had to do was draw the curse out, so there was no need for me to touch it."

"It looks like the curse is completely gone."

"It... does."

"Why didn't you take it out?"

"I... forgot."

"Good grief, you dumbass."

"What?!"

She certainly reacted quickly at times like this. I began unwinding the chain wrapped tightly around the entire tank. With every loop I removed, the flopping right arm grew more active.

"Just wait, right arm. I'll give you your freedom..."

As I was freeing it, the right arm seized the slack in the chain and leaped up. Like a carp, it struck the water's surface and launched itself straight into the bridge of my nose.

"Gack!"

While I stood momentarily dazed, the right arm dropped to the floor, stood upside down, and raced away on two fingers.

Clutching my throbbing nose, I shouted,

"Shei! Catch it!"

"Huh?"

But the Regressor had already stepped aside to avoid it. In the blink of an eye, the arm was out of the room and running down the corridor.

I hurriedly straightened up and rounded on her.

"You're just going to watch it go?!"

"It's kind of creepy... Anyway, why? It'll go find its owner, won't it? Weren't you planning to revive the undying one?"

"I was! Before she got involved!"

"Huh? What do you mean?"

"There's no time to explain! Where is Rash's body right now?"

"In the classroom cabinet."

"Why would you put him there?! No matter how you look at it, that's hiding a corpse!"

I immediately ran for the classroom, and the Regressor followed without knowing what was going on. We raced down the corridor, following the right arm's finger marks.

When we reached the classroom after our headlong dash, we found the officer standing in front of the cabinet with the bundle in her hand—and the right arm, which had kicked off the wall to launch itself through the air toward the undying one.

"My goodness. A flying right arm."

With that much control, couldn't it manage three discs too? While I murmured absently to myself,

the right arm fastened itself firmly to the undying one's shoulder. Having absorbed a great deal of the power in the Regressor's special healing potion, it transferred its accumulated vital energy into him.

It looked as if someone had plunged an enormous syringe into his shoulder. Each time the swollen arm contracted, the vital energy saturating it flowed into the undying one's body.

His body accepted that power, and as the vital energy spread through his veins, life began returning to him. Then, at a certain moment,

The undying one's eyes snapped open.