Jin began his explanation in front of the group gathered at the square before the Imperial Palace. Elsa acted as his assistant.
"I’ll give you a brief overview of the structure. First, we have the 'envelope'—the bag that holds the hot air. Any light, strong, heat-resistant fabric will work, but for this one, we used sandworm leather."
The sandworm was a magical beast native to the Shouro Empire, found in the Harihari Desert to the west. Its leather was durable enough to withstand a fair amount of impact even from Reiko.
"I see. A material sourced from our own lands," the Magic Technology Minister, Degauss, said with a satisfied nod. Jin's airship had utilized ground spider silk, a rare material that was not easily imitated.
"An oval gondola is suspended from the envelope by ropes. That’s the basic construction. Next, I'll explain how to operate it."
Jin pointed to the magic tool installed beneath the envelope.
"It utilizes the Craft Magic 'Heat' and is powered by a fire-attribute magi-stone. To use it, you simply move this lever."
Raising the lever on the magic tool heated the air, while lowering it stopped the process. By adjusting the lever to the appropriate position, the pilot could maintain a relatively constant altitude.
"I see. An application of the principle that heated air becomes lighter. I only just learned that from the Fuhrer the other day."
It seemed the Fuhrer was successfully imparting knowledge, just as Jin had intended.
"As a precaution, it’s best to have someone on board who can use 'Heat' magic. Since it’s both a Craft Magic and a beginner-level fire-type spell, quite a few people should be able to manage it."
"Indeed. About one in three magi should be capable," Degauss confirmed.
"And this is the propulsion system for this hot air balloon, the 'Wind Thruster'."
Jin had decided on a formal name for the device he had previously called a magi-propulsion unit.
"It utilizes a 'Blower' effect. By narrowing the airflow, it generates propulsive force."
As Jin had verified long ago, standard wind magic was designed to negate recoil. However, if the generated wind was funneled through a cylinder and the path was narrowed to increase the wind speed, recoil equal to that increased speed would be produced.
Because of this, the balloon could achieve speeds up to three times faster than the hot air balloons used by the Unifilar, which were largely at the mercy of the wind.
"With a tailwind, the Wind Thruster should allow you to exceed fifty kilometers per hour. In windless conditions, it should manage about thirty."
"Mm, that is plenty fast. Since it travels through the unobstructed sky, it should be quite efficient."
"Yes. However, you must not push your luck if the wind is too strong. That is dangerous."
"I understand. We shall be careful."
"Also, for emergencies, we’ve prepared arrows with ropes attached. You can fire these into the ground with this bow to serve as an 'anchor'."
"I see, much like a ship's anchor."
After explaining the finer points of operation and various precautions, Jin decided it was time for a test flight.
Chancellor Jung Fowles and Magic Technology Minister Degauss boarded one balloon. Jin, Reiko, and Elsa boarded the other to accompany them.
The Empress had expressed a strong desire to ride as well, but after being cautioned by the chancellor, the Magic Technology Minister, and the royal ritter captain, she reluctantly remained on the ground.
"Now, please push the lever all the way up."
Jin activated the heating device on their balloon. Following his lead, Degauss pushed his lever up as well.
The heating began immediately. Through the 'Blower' magic embedded in the device, hot air began to fill the envelope. It inflated before their eyes.
Once the envelope was fully rounded, it began to lift slowly. The tethering ropes pulled taut, and the gondola swayed. As more hot air was pumped in, the lightened envelope finally lifted the gondola, and the hot air balloon left the ground.
"It's floating! Ah, it's drifting away... I really wanted to go..."
The Empress watched the hot air balloon's departure with a look of longing.
"Your Majesty, please consider your position..." the royal ritter captain said in a weary voice.
＊ ＊ ＊
"I simply must ride it! I'm begging you!"
As soon as the chancellor and the Magic Technology Minister returned to the ground after getting a feel for the controls, the Empress pleaded with everyone present, her hands pressed together in prayer.
"I was allowed on the airship last time, but it only hovered a meter off the ground before it was over! This time, I want to actually fly!"
"Your Majesty..."
The chancellor and the Magic Technology Minister, having just returned from their journey through the sky, could sympathize with her desire.
"..."
After deep deliberation, they reached a conclusion.
"Your Majesty, if we tether the two hot air balloons together with a rope, I believe we can mitigate most of the risk."
Their reasoning was that even if one balloon began to fail, the other could support it and slow the descent.
"To keep the weight to a minimum, we shall have Lord Jin, Your Majesty, and Reiko-san the automata on one. We will have Degauss board the other."
This was the chancellor's ultimate concession.
"Oh, that's perfect! I finally get to fly!"
"Listen well, you must not get too carried away. Lord Jin Nidou, I leave Her Majesty in your care."
"Y-Yes."
Jin boarded first and offered a hand to the Empress. She joyfully took it and stepped into the gondola. Reiko followed, closing and locking the door behind them.
"Well then, here we go."
Jin signaled to Minister Degauss in the adjacent balloon and pushed the heating lever to its maximum. Both balloons inflated simultaneously.
Jin then ordered Reiko to provide auxiliary heating, as their balloon was carrying more weight. Reiko assisted using 'Heat' magic. Before long, the balloons lifted off the ground.
"We're flying! We're actually flying!"
The Empress was frolicking like a child.
The balloons ascended slowly. At an altitude of about thirty meters, Jin slowed the ascent and activated the Wind Thruster.
"Wow, we're moving."
The two tethered balloons drifted toward Lake Tosmo. Their altitude continued to climb slowly, reaching about fifty meters.
"Given how this works, staying at a perfectly constant altitude is a bit tricky," Jin explained, giving her a few pointers on operation.
"I see. If we go too high, we lower the heat to descend, and if we get too low, we turn it back up to rise again."
The lush blue waters of Lake Tosmo appeared in the distance. The flight had stabilized, so Jin entrusted the controls to Reiko.
"Reiko, take over for a while."
"Yes, Father."
Jin had sensed that the Empress wanted to talk.
"Thank you, Jin-kun. Ah, my wish has finally come true. The world is so vast..."
Looking down at her empire from the open sky, the Empress thanked Jin with a voice full of emotion.
"...After this, you intend to gift the same devices to the Klein Kingdom and the Kingdom of Egerea, don't you?"
"Yes, that’s the plan."
"I understand why, but I find it a little regrettable. I can't help but wish our country were the only ones to have them."
Sensing that Jin was about to respond, the Empress immediately retracted her statement.
"No, I shouldn't say such things. Now is a time when every nation must join hands to face the demon race."
"...Yes."
"In the Great Magic War, we barely managed to scrape by with a victory, but in truth, both sides were devastated. I wonder... what will happen this time?"
"I think if we understood the demon race's objective, we might be able to find a way to reconcile," Jin said, offering his opinion to the anxious Empress.
"You're right. We are all fellow beings living on this same earth. But those are my personal feelings. As an Empress, I have a duty to protect my people. At the very least, if war does come, I must be prepared to minimize the suffering as much as possible."
Jin felt the same. He viewed the various facilities on Hourai Island as military power meant for defense, not aggression.
The two balloons reached the skies above Lake Tosmo in silence. Since there was almost no wind today, their current speed was around twenty-five kilometers per hour. Deciding it was time to head back, Jin reversed their direction.
"Oh, are we going back already? I wanted to stay up here longer, but I suppose it can't be helped."
"Yes, please be content with this for today."
In the balloon tethered alongside them, Minister Degauss had a look of sheer relief on his face.
"...Say, Jin-kun. Do you have any intention of getting married?"
The Empress suddenly changed the subject.
"Eh? U-Uh, well. Not for the time being."
Caught off guard, Jin replied with a hint of fluster.
"What about Elsa? Is there nothing going on with her?"
"There is nothing!" Jin denied it with all his might.
The Empress tilted her head, watching him. "Really? I think she's quite a lovely girl..."
"Elsa is a sister figure to me."
But the Empress was persistent.
"You say sister, but you aren't related by blood. Could it be you have someone you like in another country?"
"...Why would you ask that? There’s no one."
"Well, you see, I thought the best way to keep you tied to the Shouro Empire, Jin-kun, would be to have you marry a girl from our country..."
"...Please, give me a break..."
Jin declined, explaining that while he understood her sentiment, he would be troubled by such talk.
"But really, at your age, it wouldn't be strange for you to have a wife. I mean, it's not like you're uninterested in girls, right?"
The Empress's questioning grew increasingly dogged.
"To be honest, I don't really have much in the way of those kinds of desires," Jin confessed truthfully.