Mamono-kun

When Spider Witch-san politely declined Mamono-kun's request to conduct an ecological survey of Okutama, he reluctantly backed down. He then dried his wet body with a towel and changed into loose-fitting long pants and a T-shirt. In no time, he transformed from an ordinary kappa yokai into a kappa yokai who had tried and failed to blend into modern society.

Even while pulling his clothes on over his swimsuit, he stubbornly refused to remove his kappa headpiece, so curiosity got the better of me and I asked him.

"Aren't you going to take off that headpiece?"

"No, I don't think I will. It's part of my body."

"It's part of your body?! Then are you a wizard? A kappa demon?"

"You know about kappa? How unusual. I am indeed a demon, but... It seems there has been some misunderstanding. I'm terribly sorry to shatter your dreams, but I am not a kappa. I do like kappa, but unfortunately, their existence has never been confirmed. When I say this is part of my body, that is merely a figure of speech. It is a headpiece. My real face is that of an ordinary human."

"Oh. So you're not a kappa..."

"No, I am Mamono-kun, and I don't have a real face, though."

Mamono-kun politely explained himself while saying something contradictory.

In other words, he was like a theme-park mascot. There was no person inside. Got it.

"I had imagined that the children of Transcendents became grotesque beings, but Mamono-kun is normal."

Mamono-kun's head was completely that of a kappa, but everything below his neck was human.

If that head was also a headpiece and his real face was ordinary, then his natural appearance would be that of a completely normal human.

Actually, just as he said, Mamono-kun was Mamono-kun, so he probably didn't have any such thing as a "natural appearance," right?

The Flower Witch's child and Tsugibi and Hiyori's child were unmistakably grotesque. I had somehow imagined that all demons were inhuman, but apparently that wasn't necessarily the case.

Mamono-kun's headpiece had been made with incredible precision, elaborately detailed and fitted snugly to his skin, so it was easy to tell from his expression that the kappa found my words puzzling. If anything, it was easier to read than a human's expression.

"Could it be that you don't know what a demon is, sir?"

"A child of a Transcendent, right? Ah, no, I feel like I heard a different definition somewhere, too."

"The definition was different in the past. Apparently, your definition was correct until about fifty years ago. If I may, I would like to explain it to you. It could cause trouble otherwise."

With that, Mamono-kun carefully taught me "What Is a Demon?"

A demon is "someone who can control mana, possesses a Gremlin from birth, and descends from a human bloodline," and demons can be broadly divided into two types.

The first is a child of a Transcendent.

Fuyou, born through the Flower Witch's self-pollination, possessed a Gremlin from birth. It was hidden beneath her petal skirt. The Fire Lizard also possessed a Gremlin, in its abdomen as a youngling and near its chest after reaching adulthood.

They can control mana, and their Transcendent parent was originally human.

Therefore, the children of Transcendents belong to the human bloodline and are demons.

The other type is a child of a monster tamer.

The children of people who have undergone Gremlin implantation may be born with Gremlins.

Those who are born with Gremlins through this process and can control mana are also unquestionably of human blood, and are therefore demons.

Mamono-kun was born a demon because both of his parents were monster tamers from Hokkaido who had undergone Gremlin implantation.

However, having parents who have undergone Gremlin implantation does not guarantee that a child will be born a demon. Although the birth rate has been rising year by year, the probability remains extremely low. The demon population is not large.

"How low is low? It's only been about ninety years since the Gremlin Disaster. Even with a low probability, wouldn't generational turnover have replaced quite a few ordinary humans with demons by now?"

"Oh, are you interested? This gets a little complicated, but I would be delighted to discuss the technical details. I'm very happy that you take an interest in this sort of subject."

When I raised my hand to ask a question, Mamono-kun eagerly went into greater detail.

When I sat down by the riverbank to listen to his lecture, Spider Witch-san silently lent me one of her forelegs, so I sat on it.

Years of research by countries around the world had established the patterns governing demon births.

First, as an absolute rule, at least one of the parents must have undergone Gremlin implantation. The longer the implantation period, the higher the demon birth rate.

If one parent has had a Gremlin implanted for one year, the probability that the child will be born a demon is 0.01%.

If both parents have had Gremlins implanted for twenty years, the probability is 0.4%.

Demons are born only with a low probability, but the children of demons are highly likely to be born demons.

If only the mother possessed a Gremlin from birth, the child inherited it with a 90% probability.

If only the father did, it was 5%.

If both parents possessed Gremlins from birth, inheritance was 100%.

"Huh. So it's almost entirely dependent on the mother. That's kind of like mitochondria."

"!? Sir, you are quite knowledgeable about classical biology. Do you happen to teach at a university somewhere? Are you a specialist in biology from the old era?"

"Mamono-kun-san, he's family to the Blue Witch. There are all sorts of things going on with him..."

Mamono-kun latched onto my offhand remark, and I panicked for a moment, but Spider Witch-san came to my rescue and defused the situation.

Oh, crap. The standards for knowledge had changed a great deal in eighty years.

High-school-level biology from before the Gremlin Disaster was now considered university-level. What a pain.

I seemed to have become relatively smarter, but in exchange, I knew little about knowledge that was obvious in the modern era, like demons. On balance, I suppose it evened out.

I had associated Mamono-kun's explanation with mitochondrial inheritance, and apparently there really was such a theory.

In broad strokes, humans had originally been pathetic creatures with nothing but low-spec, lousy cells.

However, during the course of evolution, they fused with primitive life. They became powerful humans with high-spec cells.

A similar event—an evolutionary transformation at the level of living organisms—was happening right now.

Gremlins are a kind of organism.

They feed on electricity and grow, spreading and reproducing by scattering something like spores.

Just as organisms had improved their capabilities by fusing with mitochondria, demons could be said to be beings who had improved their biological capabilities by fusing with Gremlins.

Demons born from Transcendent parents cannot reproduce, but demons descended from Gremlin implantation can. Therefore, it is said that humans (Homo sapiens) will gradually be replaced through generational turnover by demons (Homo Magia) and eventually go extinct.

The total demon population was currently around twenty thousand.

However, the rate of increase was gradually accelerating.

Demons did not possess as much mana as Transcendents, but they had more than humans and could control mana. Although they could not produce sounds that humans could not pronounce, they could fairly be called a superior version of old-style humanity.

Most countries, including Japan, had policies that favored demons to one degree or another.

Subsidies and incentives for marriages between demons.

Support for demon childbirth and child-rearing.

Some countries even operated sperm-donor programs.

In some countries, that would make them an aristocratic class.

So did that mean Mamono-kun was a member of the aristocracy in some countries?!

Even though he was a weird guy wearing a kappa headpiece and wrestling monstrous fish in a river?

Although, judging from his lecture, he really was an intelligent scholar.

What sort of intellectual refuses to remove a kappa headpiece? The kappa style was far too distracting.

"Since demons receive preferential treatment in marriage, are you married too, Mamono-kun?"

"Ah... I had a relationship like that once. The first ended over an affair. The second made it as far as an engagement, but the other party was the one who demanded that we call it off. Still, given how I dress, I can't say I blame them. I'm single."

That romantic history sounded awfully familiar...

I decided it would be safest not to touch that subject.

Let's talk about something else.

"Changing the subject, where did you get that kappa headpiece? I can tell it was made by a renowned craftsman."

"Oh, I made it myself."

"You made it yourself?! M-Mamono-kun-san!"

A wealth of biological knowledge.

A passion for hands-on fieldwork.

The skill of a craftsman capable of making an astonishingly detailed headpiece himself.

He was a man worthy of respect. I had to address him as Mamono-kun-san.

"May I take a look at your headpiece? Well, not just a little—may I examine it thoroughly? I'll take a look. Oh. Oh, oh, oh. Even the inside is fully detailed... Whoa, the texture is incredible! The scales look hard, but they're moist and squishy when touched! And each individual scale has a core inside. You can't even tell from the outside that you've gone this far... Wait, did you even reproduce the structure of the nostrils in the beak? You didn't just punch holes through it. I see, I see! This is based on the theory that, if kappa really had a sense of smell, this is what the shape of their nostrils would be, isn't it? This quality more than makes up for the slightly rough stitching. This isn't mere cosplay—the headpiece has a biological feel to it! It's almost as if it's really alive!"

I became absorbed in examining all the knowledge, ingenuity, and craftsmanship packed into the super-high-quality kappa mask, and only after I had examined every last bit of it did I suddenly come to my senses.

Then my face went pale.

Oh, crap.

Had I done it again?

I thought I had learned through the Hiyori massage incident that examining people without permission was unpleasant for them.

"Oh, um, Mamono-kun-san, I'm sorry for suddenly getting so handsy. That was terribly rude of me..."

"Not at all. I'm glad you understand the appeal of kappa. Truly. People who know what a kappa is are quite rare, after all."

I had surely been extremely rude, but Mamono-kun-san laughed by opening and closing his kappa beak and magnanimously forgave me. Mamono-kun-san! What a big-hearted guy.

"No, it really is incredible. What did you even eat to make a mask like this? It's not just your technical skill—the ideas behind it are amazing. Anyone capable of thinking this deeply about the structure of a fictional creature must be a super-genius."

"You have a sharp eye, sir. Actually, this wasn't originally my own idea. I carefully observe and study the bodily structures of the monsters in nature, understand how they work, and simply harmonize and incorporate them.

Monsters always grant the wisdom of nature and magic to those who seek to understand them. They truly are magnificent creatures!"

I was fired up by Mamono-kun-san's impassioned speech as he raised a fist.

"Whoa, that's badass! Learn from nature! I see. The multilayered structure of Dragon Furnace Carving is also technology derived from natural Gremlins. Honeycomb structures come from bees, and there are even sharkskin swimsuits. Using nature's technology in craftsmanship isn't anything new, I suppose."

"Oh...! You really are knowledgeable, sir! What do you say? If you have some free time, would you like to come to my place after this? I keep all sorts of monsters, and I have an interesting collection of specimens. I'll show you the natural art created by monsters."

"I'm in! Let's go! That sounds incredibly interesting!"

Mamono-kun-san gave me a gracious invitation, and I happily nodded.

However, when I tried to follow him right away, Spider Witch-san tugged me back by the sleeve.

"Hey. What about scouting for our date...?"

"Oh."

My original purpose returned to my mind, which had gone completely into craftsman mode.

The angel in my head mounted Iruma and beat him bloody while whispering, "Make Mamono-kun-san wait. The date takes priority."

Then, date first.

Mamono-kun-san was a good person, but visiting his home would only get me excited. It wouldn't make my heart race.

I asked Mamono-kun-san for his address, promised to visit his home another day, and reluctantly parted ways with him for the time being.

At first, Mamono-kun-san had seemed like an eccentric whose nature was impossible to fathom, but after talking with him, I realized he was an eccentric I could actually understand.

We got along well, and maybe—just maybe—I might make a friend about eighty years younger than me.