The Chant Harmony Score remained popular for nearly a year before something else finally stole the spotlight.
That something was the Twelfth Division's latest research project, the Spiritual Power Tester.
The finished Spiritual Power Tester was a sphere small enough to hold in one hand. Its internal structure had two layers: the outermost layer was hollow, as was the space at its center. Six channels ran through the solid structure, connecting them from above, below, left, right, front, and back.
To use it, you filled the sphere's outer layer with Spiritual Power, then squeezed it inward through the six channels. Once you had filled the inner space with Spiritual Power, the sphere would change color. At that point, you could keep squeezing until you reached your limit.
Then the main unit at the Twelfth Division would display various numbers representing your different attributes.
Jun had also suggested separating the testing device from the main unit. Like the Communication Tag before it, these were things that did not currently exist in Soul Society.
Naturally, Jun was the first person from outside the Twelfth Division to test the finished product. After listening to the instructions, he calmed his mind, focused, and began releasing Spiritual Power into the sphere.
Jun ran into trouble at the very first step. Filling the thing with Spiritual Power took a great deal of effort. He immediately increased his Spiritual Flow output, though not to its maximum, using roughly seventy percent of his strength. That greatly increased the speed at which he filled it.
Then, before the outer layer was full, Jun took direct control of the Spiritual Power inside and sent it flowing through the six channels toward the center. He discovered that getting Spiritual Power into the inner space was even harder than filling the outer layer, super, super hard.
So Jun used roughly eighty percent of his Reiatsu and control. After a little over a minute, the sphere turned red.
"Is that it?"
"Oh~ about ten breaths? As expected of a genius~"
"Was that fast? How long does it usually take?"
"My lieutenant took three times as long as you to finish. Let's take a look at the numbers."
Jun went over and looked at the main unit. His Spiritual Pool was 122, Reiatsu 304, Spiritual Reach 191, Spiritual Flow 277, and Spiritual Sensitivity 403.
"What level is that?" Jun had never seen anyone else's numbers.
"A very, very high level. Everything except your Spiritual Pool should be Captain-level." As Captain Hikifune spoke, she took the sphere Jun had just used, then released a burst of Reiatsu and finished instantly. The numbers on the display changed.
Spiritual Pool 1072, Reiatsu 476, Spiritual Reach 237, Spiritual Flow 399, Spiritual Sensitivity 286.
"See? Apart from Spiritual Pool, my numbers aren't that different from yours. Spiritual Pool takes time to build up, so there's nothing to be done about yours being low. Sigh~ looking at these numbers, I can't help thinking about my age~"
As she spoke, Captain Hikifune pinned Jun down. "You bad boy, how could you hurt my feelings like this~?"
You're hurting my face, too. Jun's thoughts were full of mischief before Isuzu pulled him away.
Kirio Hikifune didn't mind and continued explaining to Jun, "We've been testing this for quite a while now, and we've found that Spiritual Pool is the easiest to increase. It can go up by a few points every month. Of course, there are differences in talent, but they aren't too great. For the remaining attributes, though, talent plays a very large part. You can certainly increase the numbers through hard work, but it's very, very slow."
"That's no reason not to work hard, though. Compared to Spiritual Pool, the last four attributes are actually the markers of combat strength. Only with high Reiatsu can you have high output and keep others from blocking you easily. High Spiritual Reach boosts detection and communication, making someone good at relaying information. High Spiritual Flow means greater stability in battle, while high Spiritual Sensitivity lets skills take shape faster and deliver greater bursts of power."
Jun was talking about what was needed in actual combat. Whether it was Kidō or a Zanpakuto skill used after Shikai or Bankai, the essence at the core of a skill's release was Spiritual Power. That would never change.
Higher Reiatsu meant more densely concentrated Spiritual Power. When energies clashed, the Spiritual Power in a skill with higher Reiatsu was harder and sturdier. Given the same amount of energy, a blade, or technique, forged from high-grade steel, or strong Reiatsu, would inevitably defeat one forged from low-grade steel, or weak Reiatsu.
With high Reiatsu, spending 300 mana produced 300 attack power. With low Reiatsu, spending 300 mana produced only 100 attack power. That was how it worked.
Spiritual Reach mattered for commanders and messengers sending signals to attack or retreat. Increasing the speed of communication could effectively improve a group's combat strength.
Take modern information warfare, for example. With satellites in the sky and Wi-Fi on the ground, orders at every level could be directed to individuals. Send in any first-rate modern force, and even with the same equipment, it could utterly rout the most elite troops of World War II.
In gaming terms, the advantage of a wallhack hardly needed proving, did it? Streamers were often seen killing cheaters, but that was because those cheaters were too bad. Most of the time, most streamers were slaughtered at will by cheaters, which was why killing one made for such an exciting show.
Spiritual Flow determined the intensity of one's output in battle. It looked similar to Reiatsu, but was fundamentally different: Reiatsu determined the strength of a technique, while Spiritual Flow determined the strength of the person.
High Spiritual Flow meant high output per unit of time. Although higher Reiatsu would inevitably defeat lower Reiatsu, as stated earlier, that assumed they were of the same order of magnitude. Quantitative change leading to qualitative change was a truth. A high-Reiatsu technique really couldn't be blocked, but if Spiritual Flow was lacking, the technique would form slowly. If you spent half an hour on a single chant, who could you beat?
With high Spiritual Flow, you supplied 100 mana per second while casting, so a skill costing 300 mana took three seconds. With low Spiritual Flow, you supplied 50 mana per second, so the same skill took six seconds. The difference was obvious.
Spiritual Sensitivity, meanwhile, was the strength of one's technique. It was a rather abstract concept. Consider two skills: Getsuga Tenshō and Five Dragon Destruction.
Getsuga Tenshō was an ability that required very little technique. It was entirely a combination of Spiritual Flow and Reiatsu, and its power had already been demonstrated.
Five Dragon Destruction was Hadō number ninety-nine. Releasing it required Spiritual Power to flow through more than forty nodes, each of which maintained and amplified the Spiritual Power. The end result was that Five Dragon Destruction was far more powerful than Getsuga Tenshō in its normal state.
So which was stronger, a person using Getsuga Tenshō or one using Five Dragon Destruction? Some would say Five Dragon Destruction, since Aizen was stronger, but that was Aizen. Replace him with someone whose Spiritual Sensitivity was insufficient, who needed half an hour to cast Five Dragon Destruction—not because of insufficient Spiritual Flow, but simply because their control over Spiritual Power wasn't up to par.
For example, have Ichigo Kurosaki fight Ichigo Kurosaki, one using Getsuga Tenshō and the other using Five Dragon Destruction. Ichigo Kurosaki's Spiritual Pool, Reiatsu, and Spiritual Flow were absolutely sufficient to release Five Dragon Destruction, but which Ichigo would win? Anyone with a working brain would pick the one using Getsuga Tenshō, because Ichigo Kurosaki didn't know Five Dragon Destruction. Even if you made him study it, he couldn't have learned it during the period covered by the original story. Ichigo Kurosaki only knew crude, brute-force techniques; he just charged in.
So it wasn't that Ichigo Kurosaki didn't want to use other techniques in the original story. From beginning to end, Getsuga Tenshō was the only one he knew. He had that one move.
Dividing a Kidō spell's power by the amount of Spiritual Power used produced a new number: its power-to-Spiritual Power output ratio. As the Shiba Branch Family's secret technique, Getsuga Tenshō had an output ratio roughly equivalent to a Hadō in the eighties. Yet learning a Hadō around that level took even geniuses like Jun and Aizen more than fifty years, while Ichigo's Getsuga Tenshō came built in.
Seen that way, there was no need to debate Ichigo Kurosaki's Spiritual Sensitivity. Even if it was higher than both Jun's and Aizen's, it wouldn't let him use skills other than Getsuga Tenshō. There was only one reason: time wouldn't allow it. To have Ichigo Kurosaki grow to his original-story level according to the timeline, he could only use Getsuga Tenshō for his entire life.
The Spiritual Power Tester was bound to become a sensation. Everyone wanted to know their numbers so they could develop more effectively, and people streamed into the Twelfth Division.
Under those circumstances, the First Division suddenly ordered everyone to go to the Twelfth Division for testing in batches, division by division. The data would not be made public, and those on missions in the World of the Living would be dealt with when they returned.
Private discussion wasn't forbidden, though, so Jun learned some numbers and also got the baseline values from Captain Hikifune.
The baseline values represented an ordinary person's level, derived from a large body of data. Since Spiritual Pool depended on time, there was no need to include it. Reiatsu was 165, Spiritual Reach 113, Spiritual Flow 186, and Spiritual Sensitivity 84. Spiritual Sensitivity really was only in the double digits. Now, a look at some of the individual data Jun had obtained.
Ise Jun (Kiyoshi Shimizu): Spiritual Pool 21, Reiatsu 237, Spiritual Reach 196, Spiritual Flow 154, Spiritual Sensitivity 308.
These numbers were very similar to Jun's, as expected of his blood-related younger sister. Both siblings had overwhelmingly strong Spiritual Sensitivity, and theirs could still improve. Jing would inevitably become an advanced Kidō user in the future, too. Unfortunately, her Spiritual Flow was a little low, so that would need targeted training.
Isuzu Takasugi: Spiritual Pool 203, Reiatsu 171, Spiritual Reach 109, Spiritual Flow 227, Spiritual Sensitivity 121.
Her Spiritual Flow was very high. Although her Spiritual Sensitivity was somewhat lower, it wasn't actually all that low. Jun knew many people had only double-digit Spiritual Sensitivity, so reaching triple digits was pretty good. Lingling's numbers were also surprisingly impressive for combat because of her high Spiritual Flow.
Nana Onibe: Spiritual Pool 227, Reiatsu 204, Spiritual Reach 89, Spiritual Flow 198, Spiritual Sensitivity 46.
These were realistic numbers, representative of most Soul Reapers, and not bad at all. Nana's Spiritual Sensitivity meant she would be a crude, brute-force fighter like Ichigo. She could forget about using advanced Kidō in this lifetime.
Isshin Shiba: Spiritual Pool 672, Reiatsu 481, Spiritual Reach 117, Spiritual Flow 398, Spiritual Sensitivity 112.
After learning Isshin's numbers, Jun finally understood why the Shiba Branch Family had a secret technique like Getsuga Tenshō. With those attributes and that inherited talent, it would be a waste for his family not to use crude, brute-force techniques.
Shunsui Kyōraku: Spiritual Pool 1379, Reiatsu 436, Spiritual Reach 337, Spiritual Flow 428, Spiritual Sensitivity 311.
These were the most impressive numbers Jun had learned so far. Shunsui Kyōraku deserved his reputation as a genius, and his attributes were balanced; he excelled at both Kidō and the Zanpakuto. The original story also described Kyōraku as having an ocean of Reiatsu. His Spiritual Pool was even larger than Kirio Hikifune's, yet Hikifune was several hundred years older than him. Kyōraku really did have an ocean of Reiatsu.
But although Kyōraku's Spiritual Pool was larger than Kirio Hikifune's, Hikifune later went to the Zero Division and invented a special technique. As for Spiritual Pool alone, Jun wasn't sure whose would be larger at that point.
"So what are your numbers?"
"Weren't we told not to share them?"
"Cut the crap."
"You tell me yours first."
"122, 304, 191, 277, 403."
"Those numbers are fake, aren't they?"
"Seventy to eighty percent of my strength."
"298, 211, 234, 231, 287."
"How fucking much have you been hiding!?"
"About fifty percent."
"Did you hide your Spiritual Pool too?"
"How do you hide your Spiritual Pool?"
"It's a data calculation. Anyway, if the numbers after it aren't real, your Spiritual Pool has to be wrong too."
"Then yours is wrong as well."
"Yeah."
"Let me calculate." Jun's fingers moved as he rapidly worked it out in his head. "422, 234, 462, 574. Are you seriously that freaking strong!?"
Aizen looked at the numbers and tilted his head. "The Reiatsu is probably right. Spiritual Reach can't be hidden, just like Spiritual Pool, so that seems right. The Spiritual Flow number should be right. I'm not too sure about Spiritual Sensitivity, but it's probably about right. What? You only used seventy percent of your strength yourself. Work it out, and your Spiritual Sensitivity is about the same as mine."
"Then why don't you mention the others?"
Aizen was somewhat puzzled. "Isn't it only natural for your Reiatsu and Spiritual Flow to be lower than mine? I've lived more than eighty years longer than you, after all."
"Uh, okay~"
"Hehe, umm, those numbers of yours are impressive~!"
"Not as impressive as yours. You're even stronger than Shunsui Kyōraku."
"Oh? Really?"
"I don't know. Anyway, the numbers Shunsui Kyōraku gave me are lower than yours."
"They're probably fake. Let's say he used seventy percent of his strength."
"Umm, sure. Then how many years do you think it'll take you to catch up to and surpass him?"
"Three hundred years?"
"Then about the same for me?"
"I don't know. Maybe a little faster."
Listening to him, Jun flopped down on the tatami. "Sigh~ three hundred years~ that's so long."
"Yeah." Aizen's eyes lost focus, and the two geniuses who recognized each other's abilities each thought about their own affairs.