Muscles never betray you. No matter how dire the situation, muscles can turn it around. A great person of the past once said so. And, in fact, that is my favorite quote of all time.

My name is Alicia. I’m ten years old, the eldest daughter of the King of Luminaria. In simpler terms, I’m a princess.

Although we call it a “kingdom,” it’s really just in name. Ten years have passed since the great empire that once ruled this region was overthrown by rebel forces. Various feudal lords declared independence, and now there are fifteen small and large kingdoms jostling for power in what is effectively an age of war.

Among them, the Kingdom of Luminaria is a small, weak nation. We’ve been forced to grovel before neighboring kings in diplomatic negotiations time and again. Even trying to find a husband for me at the tender age of ten is merely to ensure the kingdom’s survival.

“Please! Please reconsider! Marry Alicia! Please do not annul the engagement!”

My aged father, trembling with humiliation, prostrated himself before a conceited, handsome prince with trademark golden hair neatly parted to the side—a real dandy sort of fellow.

I, strapped into a corset to fit into a dress that looked good but was restrictive and hard to move in, watched from a distance, feeling wretched and embarrassed. Being made to wear such attire in the first place was a constant reminder that women in this era were little more than pawns in political marriages.

“Absolutely not,” the dandy said. “I’ve decided to marry a princess from a stronger country. What does your domain have, anyway? There’s a tiny iron mine, but it’s so worthless it can hardly produce anything. It’s only a matter of time before one of the neighboring kingdoms wipes you out.”

“Please, please! Alicia, you bow as well,” my father pleaded.

Given how my father, who had cared for me all my life, had cast aside all pride and lowered himself this far, I had no choice but to do the same, even though I knew the man before me was dreadful.

“Hngh… Very well. I beg you as well. Since my father is pleading so earnestly…”

“No can do. I, Prince Johnny of the mighty Kingdom of Barigos, am a realist. I won’t give in to tears or heartfelt pleas. Wealth—that’s what matters. If you want to marry me, make your country wealthy first and then come back.”

And with a spit on the ground, the conceited prince turned and left. Honestly, I was relieved I didn’t have to marry someone like that. Still, I couldn’t help but feel furious, wanting to prove him wrong someday.

“Ugh, how infuriating! The only way to clear my head is with a circuit workout—push-ups, sit-ups, back extensions, squats, high-knees, and, and…!”

It was frustrating that, no matter how much I trained this small female body, it remained weak compared to what I desired.

In my previous life, I had been a man. I lived in Los Angeles in the United States, studying health at university while competing in bodybuilding contests. One day, I died in a traffic accident. All the muscle I’d trained so hard to build was powerless before solid steel.

And now, by some twist of fate, I was reborn into this fantasy world as the princess of a weak kingdom.

After the shock of the broken engagement and endless demands of our impoverished kingdom, my father’s health failed him. With no male heir, once my father breathed his last, I became queen at only ten years of age. Granted, someone called a regent would hold the real power, given that I was still a child.

Honestly, when I first heard about this, I worried they would keep me locked away in a dark room like a puppet, a figurehead for a puppet regime.

However, Artemis—only sixteen years old when he became regent—did not go that route. People realized the kingdom’s weakness stemmed in part from the severe aging of those at the core of government, so there was growing momentum for a new generation to take over. Because of that, Artemis was keen to adopt ideas from someone as young and untested in life and learning as I was.

One day, Artemis came back from inspecting our mine, scratching his head in confusion.

Stolen from Royal Road, this story should be reported if encountered on Amazon.

“This is strange. Scholars have said the mine’s potential reserves are considerable, but we’re not seeing any increase in output at all. What on earth is going on? Are the scholars lying?”

Watching the miners at work, I commented,

“None of them have nearly enough muscle to do efficient mining. Their faces are pale, and this region is often covered in fog, which means they’re low on serotonin. If they had more sunlight and protein, it would solve the problem. And given the amount they sweat while doing physical labor, they need minerals, too. Look—some of them are having nasty leg cramps.”

I spewed out health and sports science jargon that made little sense to people of this world. Artemis listened, nodding along, though I couldn’t be sure how much he truly understood.

“So basically, what should we do?” he asked.

“This kingdom is inland, but there’s a friendly nation that’s rich in seafood, correct?”

“Yes, we usually export iron to them, and in return, we import their famous fabrics. We sustain ourselves on agriculture here, so we’ve never bothered to import seafood. I mean, we don’t really need it.”

“In that case, let’s do this: import seaweed and shellfish and feed them to our laborers. That should reduce the leg cramps.”

“Do you really think importing that stuff will help…?”

Although Artemis sounded skeptical, he accepted my policy. In that friendly nation, seaweed and shellfish weren’t part of the local diet. They were simply discarded when fishing for herring, so we could obtain them at virtually no cost.

On another day, a man claiming to be a sailor visited the castle for an audience.

“My Queen, I come bearing a rare curiosity. This is a creature called a ‘chicken,’ which I acquired from the natives of the subcontinent. I present it as tribute.”

“Cluck, cluck, cluck!”

Apparently, in this world, chickens are still newly discovered creatures.

The sailor continued,

“Quite an unusual call, don’t you think? If you show it off at fairs, you could make some money and boost tax revenue.”

“Question,” I said. “Does that animal lay eggs?”

“W-well, yes. They lay large white eggs and quite a lot of them, too.”

“I see. And how widely known is this animal in other nations?”

“This is the third country I’ve visited after returning from my voyage. The first two just laughed in my face and sent me off.”

I smirked inwardly. In this world, chickens are seen as rare oddities. Other countries think so little of them that they don’t bother. But I realized just how valuable they could be in building our national power. Eggs are highly nutritious and full of the protein needed to build muscle. Roosters can be used for meat. It’s perfect for improving the health and strength of our miners. This was a chance for technological innovation.

“Then we shall raise these chickens here in the Kingdom of Luminaria. Not as sideshow attractions, but as an essential food resource.”

Somewhat surprised, the sailor nevertheless bowed deeply. “Understood.”

By raising chickens and incorporating eggs into the workers’ diet, we could boost mining efficiency. Securing a self-sufficient source of protein would solidify our kingdom’s foundations and set us on the path to becoming a stronger nation.

Artemis agreed with the plan and immediately ordered the construction of a chicken farm. Thus began my “protein plan” to strengthen the kingdom, founded on my belief that “muscles never betray.”

To address the foggy conditions in our mines and the resulting lack of sunlight, we introduced communal land use and a rotation system for farmers and miners. This should help alleviate vitamin D and serotonin deficiencies.

Moreover, drawing on the latest sports medicine from my previous world, I incorporated a series of stretches. For physical laborers, we focused on exercises to keep their hip joints limber; for desk workers, we developed a curriculum to prevent poor posture, reminding them to keep their backs straight.

Productivity among workers clearly rose. The laborers who would tire out quickly now seemed to have more energy. The infant mortality rate dropped significantly, and in the medium to long term, there were indications of population growth.

With increased iron output and a workforce fortified by muscle, we also achieved higher agricultural production. Livestock farming developed into a major industry. As the people grew more prosperous, they had time to enjoy culture and scholarship. A massive library was built, and we even had scholars who solved the perennial issue of flooding in our rivers through civil engineering projects.

The military also adopted circuit training based on sports science, along with new exercise equipment, allowing our troops to keep pace with the armies of other nations. Our soldiers could rapidly shift into battle formations once considered theoretically possible but practically unworkable, marking a generational leap in military technique.

Buoyed by this newfound wealth and military strength, our diplomacy grew ever more assertive, and we began to hold our own among neighboring nations. More and more of them started to regard us with respect.

And then, none other than Prince Johnny of Barigos—the one who had so arrogantly abandoned our engagement—requested an audience.

“M-my Queen, I’ve come to humbly ask if we might…rekindle our relationship.”

He was probably forced to do this by his father, and the humiliation twisted his face into a grimace.

“Now, after all this time, you want to bow to me? Too late! I’ve already decided on Artemis as my marriage partner! But if you wish to become our vassal state, bring tribute.”

By that time, I was twenty years old and carrying Artemis’s child. I would soon give birth to a prince, our heir. It felt a bit strange bearing children in this life, given that I was a man in my previous one.

In the end, I led the Kingdom of Luminaria to prosperity, gradually unifying the surrounding nations and laying the foundation for what people would come to call the “Hundred-Year Kingdom” and a long era of peace.