With his position in his immediate surroundings safeguarded, Tom found himself with a lot of free time and he intended to use it for projects he wanted to do years ago.
His father's presence and the lack of materials hindered him then... but no more.
The major problem with Vision was its cost. The magical energy necessary to use it was immense for Tom's current standards.
Using it on something mundane, like normal fruits, did cost a very little mana. Using it on something magical... the cost rose exponentially. Tom couldn't even imagine how much magic it would cost to use Vision on a magical artifact.
But using it on another human... now that took the cherry. There was never a time when Tom didn't faint while doing that only to wake up with a pounding headache that persisted for the next three days. He even used it on his father once and then dropped like a sack of potatoes in front of the man.
And even then, when he woke up, he had only a few confusing glimpses, far from a full picture.
Clearly, he didn't have enough mana to view the history of another being. Something in the makeup of the living beings was preventing his Vision from prying and to get past that, it cost more magical energy.
Tom's biggest advantage was that he was a human. He was cunning and crafty. He fully understood he didn't have much going for him and he had to make a do with what he had. He was not a supernatural race with loads of energy reserves so...
It was no surprise that his newest project was an external mana storage crystal.
Tom's initial desire was to create something like chargeable Soul Stones from the Chinese xianxia stories he was reading in his past life. It sounded amazing. A stone that could store a massive amount of Chi, aka energy, and the user could use that energy for formations, aka spells, or reabsorb it to himself to raise his cultivation, aka magic reserve.
The concept was flawless. A pity that it only worked in Tom's head.
Three weeks into his new research, he realized how hard it would be to create just ordinary mana storage. Something like what he had in mind... pfft, it was far from his reach.
First of all, Tom was not a master enchanter or alchemist. He was a novice at best. The whole reason why he could attempt to do things even masters would struggle with was that he was cheating with his Sacred Gear.
Every 'finished' product, Tom screened with his Sacred Gear... and God was there a lot of fainting for him involved... and this would give him insight into where he went wrong. Not a big insight, but at least some clue on where he went wrong was better than no clue at all.
And so, Tom would scrap the entire thing and start all over from the very beginning, implementing his new insights.
Rinse and repeat, rinse and repeat, again and again.
And eventually... aka, three months of painstaking work later... Tom finally held a finished Mana Storage Crystal in his hands. Not one that worked as he wanted it to. Heck, it barely worked for storing mana! But it was Tom's very first product that could both store mana into itself and allow the holder to use said stored mana for something.
As garbage as the storage capacity was, as garbage as the efficiency of the charging was, as garbage as the whole crystal was... It was Tom's first success and he was proud of it.
'Baby steps.' Tom thought with a silly smile plastered on his face as he looked over the small but smooth purple crystal he created. 'From here, it can only get better.' He chuckled.
...
It did get better. A lot better!
Two weeks after Tom finished his first chargeable mana crystal, he finally reached a stage where he was satisfied with it.
He improved a lot of things on it, most noticeably the charging rate and the storage capacity.
The storage capacity was... doable. It just required better, more magical materials to be used in the creation process so the crystal could hold more mana without bursting.
Sounds easy, right?
Well, if Tom didn't have his Sacred Gear and had to actually charge every crystal to see its max capacity, instead of quickly checking it with Vision, he would have to spend decades on this part.
If other alchemists knew about how Tom was cheating his way through these gruesome parts of researching, they would cry bitter tears and probably start to make plans on how to steal his Sacred Gear.
Something on that thought gave Tom an extreme case of schadenfreude.
As for the charging rate...
At first, it was atrocious. Anything he would do would improve it. And Tom was still a human with a limited lifespan. He couldn't spend years charging one crystal. Fortunately, through a copious amount of Vision usage, and trial and error and some more error, he slowly started to get rid of all the inefficient kinks in the design, improving the charging rate tremendously.
Thanks to that, it wouldn't take him ten years to charge the crystal to the full, but only a month. That's how much the efficiency improved when he was 'finished'. And by the way, that was still shit compared to even average magical artifacts.
Sure it could still get better. It always could be improved further but for now, this was enough for Tom's needs and he stopped his research on this topic.
At its max capacity, the finished mana crystal could hold the mana reserves of an Ultimate-class being. That's why it would still take a month of nonstop charging if Tom funneled into it ten percent of his reserves at all times.
The way it worked was simple. Tom's reserves would always try to recharge but any mana that would go over 90% of his magical reserves would instead go to the crystal he was wearing as a necklace around his neck.
Like this, he could amass mana comparable to an Ultimate-class being with his meager middle-class reserves.
As an unintended effect, Tom noticed his mana reserves slowly growing to accommodate this constant drain. The growth wasn't world-breaking or anything. If it continued at this rate, he might be able to gain high-class reserves in a decade or so... but it was growth for no effort and Tom would take what he could get.
With his focus being all concentrated on researching, he didn't have time to properly train. There were only so many minutes in the day and no matter what one tried, getting everything done was impossible. That's why people choose their priorities and act accordingly.
Tom could have trained for an hour a day but the returns wouldn't be anything spectacular. He simply deemed it better to spend said hour in his lab.
And what do you know? It actually paid off! From now on, he would get passively stronger despite spending most of his time researching. How cool was that!?
Needless to say, Tom was like an excited kid on Christmas Eve because of this unforeseen effect of his latest invention.
The biggest problem in the mana crystal development was how easy it would have been to detect it. With the storage capacity at the level of Ultimate Class being, the crystal would be an irritatingly bright shining spot on the senses of anyone competent.
But Tom had no way to prevent that. None whatsoever. His understanding was very small in this area and studying it from scratch would be a bother and a waste of time for him.
Tom had only one... untested method.
Namely, the array inscribed into his sacred gear to 'hide' its existence pre-awakening.
Tom didn't understand how it provided said effect but he could use the 'monkey see, monkey do' method, couldn't he? He could still inscribe the array on his product. Who cared he had no idea how or why it worked?
Okay... he was bothered by the fact a lot. But he also didn't have an alternative.
Many humans who held Sacred Gears were never discovered by supernatural forces. And that was because before the Sacred Gear awakened, its holder 'felt' in the senses of others just like a normal human being.
Naturally, there were special methods to locate these people but they took more effort and most importantly, focus than they were worth it.
An apt example would be, Azazel.
He was extremely strong and experienced, and could definitely tell if somebody had a Sacred Gear by just looking at a person. But put him in front of a town and he would not be able to tell you how many Sacred Gear holders live in it without using some kind of scanning gadget.
He needed to focus on a person to tell. Instead of brightly shining on everyone's senses, the Sacred Gear was hidden while dormant, and detecting it required one to focus on the holder.
And that was what Tom wanted to exploit. Wearing the crystal as a necklace and having it under his shirt all the time, it wouldn't grab the attention of anyone. If anyone focused on Tom, they would inspect him with their senses, not the crystal.
Unless somebody fully focused on the crystal, the 'hiding' array from the Sacred Gear would obscure it from their senses.
It wasn't a perfect solution but it was an available one.
With a plan of action decided, Tom looked at the innocently looking purple crystal on his table and wryly smiled, 'Another few weeks of research on how to inscribe the array onto the thing. Oh joy.'