Jin and his team began brainstorming ways to produce a higher-performance magi-resin.
"First, I wonder if we can improve its properties by blending in additives."
"Additives?"
"Exactly."
Magi-resin was the general term for any resin that reacted to mana, and it served as the standard internal material for most golems. The most common variety was the resin extracted from magi-pines, trees that naturally contained mana—another innovation that Adriana had once brought to practical use.
"The main goals are improving mana conductivity and increasing power output. Those are our hurdles," Jin explained.
Rubina reacted instantly to his words. "Conductivity... maybe mixing in mithril powder?"
"Oh, exactly. That's the idea."
Jin noted that while excessively expensive additives would drive up costs and hinder widespread use, that level of addition was perfectly acceptable.
"The best way to know is to try it."
With that, the group began experiments on magi-resin blended with mithril powder, with Rubina taking the lead.
The experiment of mixing mithril powder into magi-pine-based magi-resin was a modest success. The addition improved the power output by 1.5 times and doubled the reaction speed.
"I wonder if this is as far as we can take it," Rubina murmured, clearly unsatisfied.
Jin offered her a bit of advice. "Well, let's try changing our perspective. Let's look at it from a theoretical standpoint: what exactly did the addition of mithril powder achieve?"
"Hmm... the theory behind it..."
As Rubina fell into thought, Greena voiced her own speculation. "You were hoping for an effect similar to creating a magi-type alloy by adding it to metal, right?"
For better or worse, Rubina’s thinking was still very intuitive, and she seemed to struggle with purely theoretical reasoning. This was hardly surprising, given that she was only ten years old.
"So, let's reconsider magi-resin itself," Jin continued. "Why does tree sap—something essentially like pine resin—react to mana at all?"
"Um, well..."
"...Is it because some of the atoms that make up the resin have been replaced by magi-isotopes?" Greena ventured.
"Yeah, that’s likely the case," Jin agreed.
Surprisingly, even Jin didn't know everything there was to know about magi-resin. He rarely used the material in his own work, preferring more advanced alternatives.
"Therefore, the higher the concentration of magi-isotopes, the more reactive the resin should be to mana."
"Jin-sama, is that even possible?" Marikka asked. She had been listening quietly to the younger girls' opinions, but she couldn't keep silent any longer.
"Well, it's just a guess, but I'm thinking we could age the resin in a free ether box."
A free ether box was a storage container maintained at a free ether ratio of 80 percent or higher. Placing magi-type materials inside increased their purity over time as their atoms were gradually replaced by magi-isotopes.
"I didn't know such a thing existed... That's incredible!" Rubina said, her eyes wide with genuine admiration.
"The next steps would be selection and concentration," Jin added. He explained that they could filter for magi-resin with the highest magi-isotope content and then find a way to concentrate those specific portions. "I haven't quite figured out the 'how' yet, though."
"That sounds like you, Jin-sama. If that's the plan, I want to come up with something too!" Rubina chirped.
"Haha, you do have a knack for inspiration, Rubina."
The moment Jin said that, Rubina let out a cry. "I've got it! We should just run magi-circuit wires through the resin!"
"I'd love to say 'as expected,' but I've already considered that," Jin pointed out. "It would certainly increase reactivity, but the power output wouldn't change. On top of that, the crafting cost would skyrocket."
"Oh, right..." Rubina looked slightly disappointed, but she didn't let it get her down for long and immediately went back to thinking.
"Jin-sama, what if we embedded magi-stones at key points, like where the joints would be?" This time, the suggestion came from Greena.
"I actually tried that the other day as well."
"I see... You're always one step ahead, Jin-sama." Greena let out a long sigh.
"But both of you are doing great. I had to struggle quite a bit to squeeze those ideas out of my own head, you know." Jin praised them both, offering a warm smile.
"Jin-sama, instead of sticking strictly to magi-resin, perhaps we should look for a different medium that's both cheap and high-performance?" Marikka suggested.
"Yeah, that's a valid path. I tried experimenting with magi-polyethylene," Jin explained, though he noted that the results hadn't been as impressive as he'd hoped. "In the end, Ground Spider resin proved to be the best, but the cost is just too high to make it viable for this project."
As they worked through various ideas, noon arrived, and they decided to break for lunch. It was a much-needed change of pace.
"Wow, it looks delicious!"
Since Reiko was away acting as an escort for Jin D, the meal had been prepared by Luna and Soleil.
For a moment, Jin wished Mini Reiko was there, but it was impossible while Reiko was operating with Jin D. Reiko's control core wasn't designed for parallel processing; trying to control Mini Reiko as a remote terminal would interfere with her main body's movements.
Regardless, today's lunch was hiyamugi.
By late April, daytime temperatures on Hourai Island could climb near 30 degrees Celsius, making chilled noodles a very welcome sight. The white hiyamugi noodles were accented by strands of red and green, giving the dish a cool, refreshing aesthetic.
They could add eggplant or sliced cucumber to the dipping sauce as they liked. Grated janzy was also provided, which added a sharp, delicious fragrance to the broth.
Their preferences were perfectly varied: Jin stuck to the simple sauce, Rubina added cucumber, Greena went with eggplant, and Marikka added the janzy.
"Ah, that was wonderful."
After eating, they enjoyed a leisurely tea time with cold barley tea.
"It's so cold and refreshing. Can I have a refill?"
"Don't drink so much that you upset your stomach, alright?" Jin cautioned. Back in his high school days, he had once gorged himself on ice water to beat the summer heat and ended up with a miserable stomachache that ruined half his vacation.
"Okay... I'll be careful." When Jin shared his own painful experience as a warning, even the energetic Rubina nodded obediently.
Once their post-meal rest was over, they resumed the study session.
"Hey, Jin-sama, I just thought of something. When magi-resin moves, which part of it is actually doing the work?" Rubina asked.
"Which part, you say...?"
"If it were fixed to the skeleton like a muscle, the function would be obvious. But that's not how it works, is it?"
"Oh, I see your point." Jin was impressed by her perspective. "You're right. Since this is an extension of Forming technology, it should share the same characteristics."
This meant that the most force was likely being generated at the "bending points"—the joints. It was unclear how much the rest of the material actually contributed to the overall movement.
"That's an incredible insight."
Jin praised Rubina once more, and they decided to focus their research on that specific lead.