Rukia Kuchiki: "...You'd better hurry up and bring Myōki back."
In the past, whenever questions like this came up, Myōki would simply give him the answer.
Now that Myōki was gone, Muten Natsu's brain seemed to have gone blank along with it.
He could figure things out himself if he tried, but he was lazy. If he could ask someone else, he would rather not bother thinking.
"It's no surprise you don't remember much about it. This is something you've never been able to grasp," Retsu Unohana explained patiently. "Everyone's Reiatsu has its own unique nature. It simply isn't very noticeable under normal circumstances."
The Reiryoku contained within Reishi was like water. Water by itself had limited destructive power, but once pressurized, it could cut through steel.
By placing Reiryoku under pressure and giving the Reiryoku born from the Haku the consciousness of the Kon, it became Reiatsu that could be freely controlled and used in battle.
If a spiritual body were a pen, then Reiryoku would be the ink inside it, and the words written by that pen would be Reiatsu.
Everyone wrote words, but each person's handwriting had its own distinct characteristics.
Likewise, everyone released Reiatsu, but the nature of each person's Reiatsu was different.
Most of the time, those differences barely mattered.
No matter what style of handwriting someone used, being able to read it was enough.
No matter what nature someone's Reiatsu possessed, being able to defeat the enemy was enough.
But under certain circumstances, the nature of Reiatsu could have an enormous effect on how effectively it was used. Namely...
"When casting Kidō, you need to adjust the nature of your Reiatsu so that it better matches the corresponding Kidō, increasing the technique's power," Retsu Unohana explained. "You were never good at changing the nature of your Reiatsu, so it's only natural that you don't know much about it. Rukia is much more skilled in that area."
"The greatest application of changing the nature of Reiatsu is Kaidō." Rukia Kuchiki shook her head. "But the Captain is still far better at that than I am."
Muten Natsu opened his mouth. "Why is..."
Rukia Kuchiki glared at him. "Think about it yourself."
Ever since Myōki had left, it seemed Muten Natsu's brain had packed up and left too.
Muten Natsu: "..."
Rubbing his earlobe as he searched his memory, Muten Natsu finally remembered that Kaidō was also a type of Kidō.
Although both were forms of healing, Kaidō worked differently from Orihime Inoue's Sōten Kisshun. Kaidō usually began by restoring the injured person's Reiatsu, then using that restored internal Reiatsu together with the practitioner's external Reiatsu to repair the body.
To restore an injured person's Reiatsu, the nature of the Reiatsu used in Kaidō had to be altered according to the specific injury.
Retsu Unohana added, "I just tried changing my Reiatsu into various different natures, but none of them affected the connection formed by Heaven's Will's mist."
Muten Natsu looked puzzled. "Is that really impressive?"
"It means that, in theory, Heaven's Will has the ability to eliminate or neutralize the nature of Reiatsu. If used properly..." Satisfaction showed in Retsu Unohana's eyes. "You could reduce any attack that relies on the nature of its Reiatsu to nothing more than a straightforward attack."
Muten Natsu immediately realized just how significant that ability was.
Izuru Kira's Wabisuke, Suì-Fēng's Suzumebachi, Shinji Hirako's Sakanade... without the unique nature of their Reiatsu, the effectiveness of their abilities would be drastically reduced.
Put simply, Heaven's Will was the perfect answer to all sorts of fancy tricks.
It was precisely because Heaven's Will could neutralize the nature of Reiatsu that it was able to connect the spiritual energy of two different individuals, forming a tangible bond of mist through which power could be transmitted.
It was like a universal data cable.
But if it could transmit power...
Muten Natsu suddenly became worried. He raised his hand, bit the tip of his finger, then looked at Retsu Unohana and Rukia Kuchiki.
"Are you two okay?"
Rukia Kuchiki: "...Are you okay?"
Why had he suddenly bitten himself?
Retsu Unohana showed Muten Natsu her own fingertip. "It seems the connection only shares power, not injuries. I also tested something else just now. My Reiatsu only flows toward you when the amount I release exceeds yours. The same applies to the nature of the Reiatsu."
So Muten Natsu had been worried that injuries might be shared as well...
Only then did Rukia Kuchiki understand what he had been thinking. As expected, Captain Unohana understood Muten better.
Muten Natsu toyed with the mist. "The principle of communicating vessels, huh..."
"Which means something like this should also be possible." Retsu Unohana altered the nature of her Reiatsu. The blood-red mist became even more vivid, and the wound on Muten Natsu's fingertip rapidly healed. "I strengthened the self-healing nature of the Reiatsu, allowing your body to heal itself more quickly. The principle is the same as Kaidō, but this kind of healing can be maintained at any time during battle."
Muten Natsu stared at his now-healed fingertip and finally understood why Rukia Kuchiki had been so shocked earlier.
"Captain." Isane Kotetsu came over to report. "All the wounded are out of danger now, and their conditions are stable. It's all thanks to Orihime-san's help."
"Hehe~" Orihime Inoue, who was visibly exhausted, smiled. "I just did what I could... Huh? What are you three playing with?"
Noticing the mist floating between them, Orihime Inoue curiously reached out. Before she could do anything else, the pure white mist curled around her wrist, and a warm golden hue like sunlight spread through it like the glow of sunset.
"What's this?"
Orihime Inoue instinctively flicked her hand, breaking the connection and causing the mist to dissipate.
"Don't be afraid. It's an ability of Muten Natsu's new Zanpakutō, Heaven's Will." Retsu Unohana gently stroked Orihime Inoue's head. "Try recreating the feeling you just had."
"Oh, I see~"
Reassured, Orihime Inoue connected to the mist again.
Muten Natsu felt as though he were basking in the afternoon sun, warmth spreading pleasantly through his entire body.
"Ah... yawn!"
He couldn't stop himself from yawning.
He was getting sleepy.
Orihime Inoue's reaction, on the other hand, was much more dramatic.
The blue hairpin on her head visibly grew larger, releasing a sharp aura completely unlike its usual presence.
Orihime Inoue hurriedly covered the hairpin with her hand. "Th-This is...?"
Rukia Kuchiki knew quite a bit about Orihime Inoue's Shun Shun Rikka. "It looks like Koten Zanshun's power has increased tremendously."
Muten Natsu's gaze softened as he looked at Orihime Inoue.
Orihime Inoue had surely noticed Koten Zanshun's increase in power as well, yet her first reaction had not been to test how strong it had become. She had immediately covered it with her own hand.
Often, a person's instinctive reaction revealed their true character better than anything else.
"Isane." Retsu Unohana beckoned to her. "You try it too."
"O-Okay."
Isane Kotetsu reached out and tentatively grasped at the mist.
"Like this...? Huh?"
Even though Isane Kotetsu made exactly the same motion as Orihime Inoue, the mist didn't react to her at all.