"Father, what should I do?"
Reiko asked the question, wondering if she needed to accompany him as she had when they dealt with the demon race.
"I’d like you to help me with a few things here, Reiko..."
"I do not wish to leave your side, Father."
While Laozi—Laojun’s mobile terminal—was more than capable of handling the mission alone, it was always better to have a support unit.
"Alright. I’ll have Anne go this time."
Jin called for Anne.
"Master, did you summon me?"
"Anne, I’m sending you and Laozi to the town of Ismar."
"I understand. Please leave it to me."
Jin explained the details of the plan to her. Laojun followed up with supplementary information, ensuring Anne was fully briefed.
＊ ＊ ＊
After Laozi and Anne departed through the Warp Gate, Reiko turned back to Jin.
"Father, what is it you intend to do now?"
"Ah. Once Hanna is asleep, I’ll gather the others and explain."
Loizart, the capital of the Shouro Empire where Hanna was currently staying, had a time difference of approximately five hours and twenty minutes with Hourai Island. Hanna usually woke up around 6:00 AM.
This meant that when it was midnight in Loizart, it was 5:20 AM on Hourai Island.
"At 3:00 AM Hourai Island Time, the Jin Family will assemble."
In response to his call, three people gathered: Reinhard, Elsa, and Saki.
Toa and Stearena had been invited to Marquis Theoderic’s estate and were unable to slip away. Additionally, since the discussion promised to be purely theoretical, Mine, Vivienne, and Berche did not attend.
"Now then, I’ve asked you all here to discuss a theory I stumbled upon the other day."
It was still the middle of the night in the Shouro Empire, and Jin began his explanation while rubbing his sleepy eyes.
"First, I assume you’re all familiar with the Magi Jet Engine I developed."
All three nodded in agreement.
"You likely also know that it works by removing the component of wind magic that cancels out recoil."
Standard wind magic is designed to negate the recoil that would naturally act upon the caster. Because of this, no matter how powerful the gale produced, the caster remains entirely unaffected.
If that recoil cancellation is removed, the wind magic produces a physical reaction. The Magi Jet Engine was the result of harnessing that reaction as thrust.
Reinhard and Elsa nodded immediately. Saki also seemed to follow the logic, nodding with a slightly hesitant look.
"Now, here’s the main point. What happens if we do the opposite—and make it so that no wind is generated at all?"
"Eh?...I see! You’d be left with only the force that attempts to cancel the recoil, even though there’s no wind to trigger it?"
Reinhard was the first to realize the implication.
"Exactly, Reinhard. For now, let’s call that 'recoil cancellation magic.'"
"...What kind of force is that?" Elsa asked.
"Wait, wait. Is it even possible to isolate just that force?" Saki added.
"That’s exactly what I want us to investigate," Jin replied, his expression serious.
"I see. If we can pull that off, it would be a massive breakthrough!"
It could potentially revolutionize propulsion technology.
"I’ve already made some progress with preliminary experiments. Let me explain those first."
Jin produced a small magi-crystal.
"This is a magic tool that generates directional Gravity Magic."
After giving the explanation, he spoke the keyword to activate the gravity.
"It’s currently generating 1G of upward gravity. In other words..."
Jin pinched a small pebble and released it above the magi-crystal. Instead of falling to the floor, the pebble drifted aimlessly in mid-air.
"Right. It’s negating gravity," Reinhard noted with a look of understanding.
"Exactly. Now, what if I do this?"
Jin rotated the magi-crystal ninety degrees to the side. He held the pebble in front of it and let go. The pebble shot out diagonally before gravity took hold of it, pulling it down to the floor.
"Hmm. The pebble flew in the resultant direction of gravity and the magic tool’s force."
"I think I’m starting to get it, Jin," Saki said. "You’re wondering if the force that cancels the recoil of wind magic is actually the same thing as Gravity Magic, aren't you?"
Jin shook his head.
"I thought so at first, too. But it seems they are similar yet fundamentally different."
"Eh? What do you mean by that?"
"If they were the same, then the effects of Gravity Magic would extend far beyond the caster who used the wind magic, right?"
"Uh..."
Saki stared into space, her eyes wandering as she tried to digest the explanation. Perhaps Jin’s wording hadn't been the clearest for her.
Elsa was the one who spoke up next.
"If it were gravity, the effect would reach a long distance. But in reality, the recoil-canceling force only affects the caster. Is that it?"
"Exactly, Elsa. And that's what's been bothering me."
Jin emphasized the difference in the effective range between Gravity Magic and recoil cancellation magic.
"I believe that’s also why the mana consumption is so different. Gravity Magic consumes over a thousand times more mana."
"I see. So that's why you're so focused on this recoil cancellation magic, Jin."
A thousand-fold difference in efficiency was a massive factor. Reinhard now understood why Jin was pursuing this so intently.
"The difference in mana efficiency probably has to do with the range of effect," Saki said, having finally organized her thoughts.
Gravity Magic exerted its influence in a straight line from its point of origin, whereas recoil cancellation magic only applied to the caster. The difference in their respective scopes was staggering.
"Yeah, I think there's almost no doubt about that," Jin agreed.
"...Jin-nii, what exactly is 'gravity' anyway?"
Elsa asked the most fundamental question of the entire discussion. Even Jin found himself hesitating.
"Well... honestly, even I don't know the full details."
In Einstein’s General Theory of Relativity, a gravitational field is described as the curvature of spacetime itself. Jin knew this much from television, science magazines, and even sci-fi novels and anime.
However, knowing a fact and truly understanding it were two different things.
"This world has forces like free ether and mana that didn't exist in my world. I think we’re going to need a completely new theory."
Ultimately, Jin had to admit his ignorance.
"The theory is one thing, but can we actually use that force?...Actually, knowing you, Jin, you probably have some kind of lead, don't you?"
Jin gave a wry smile at Saki’s remark.
"No, I’ve actually hit a bit of a wall."
"Oh? Jin, I'd like to hear the details," Reinhard said.
"Me too."
Both Reinhard and Elsa watched Jin with intense curiosity.
"Of course. That was the plan for tonight."
Jin produced another magi-crystal.
"This is a prototype for recoil cancellation magic. But it’s a failure."
"Oh? Let me see."
Jin tossed the magi-crystal to Reinhard.
"Thanks....Hmm?"
Reinhard immediately began analyzing the magi-formula inscribed within.
"I see. This is..."
The base was the wind-attribute magic, Wind. Theoretically, if one removed the part of the magi-formula that caused the wind to blow, the recoil cancellation magic should remain. However...
"It won't activate," Jin said, his expression sour.
"Eh?"
"...I suspect it’s because it’s a magic that specifically cancels out a reaction. It seems it won't trigger unless there is an action—the wind blowing—to trigger it."
Saki and Reinhard both nodded at Jin’s hypothesis.
"I see... No effect without a cause, then."
"So even for you, Jin, it's hard to isolate the recoil cancellation magic, even if you can remove it..."
But Elsa, who had been lost in thought, suddenly spoke up as if struck by a realization.
"How does recoil cancellation magic negate the reaction with the exact same magnitude as the action?"
"What?"
"If it has to get information from somewhere and then decide the magnitude of the recoil cancellation magic based on that, I think there would be a delay."
Elsa’s observation struck Jin, Reinhard, and Saki at once. The core of the problem lay in the very point she had raised.
Magical recoil was canceled instantaneously, without a microsecond of delay, the moment the spell was cast. But how?
"That’s the part I just can't wrap my head around," Jin said, his voice laced with frustration.