Just imagining how Muten Natsu must have felt back then was enough to make Rukia Kuchiki feel as if she were drowning.
The peaceful life they had known had been shattered without warning, and of all the children who had lived together, only three remained.
They came to Seireitei. Rukia Kuchiki found her long-lost sister and became a noble of the Kuchiki Clan.
It looked as though everything was finally getting better.
And then came the news that the Kuchiki Clan intended to use Rukia to treat Hisana Kuchiki.
Hisana Kuchiki did not want to cure herself by harming her own sister, so she kept that method buried and made sure Rukia would never learn of it.
But from Muten Natsu's point of view, it looked like the Kuchiki Clan was plotting in secret.
First, they brought Rukia into the Kuchiki Clan under the name of adoption. Then, once the time was right, they would carry out the transplant.
What could Muten Natsu do?
He was only a commoner from Rukongai. Even though Retsu Unohana had helped him enter Seireitei, there was no way he could stand against one of the Four Great Noble Clans.
And as for telling Rukia Kuchiki everything...
Telling Rukia that the only family she had left wanted to harm her was simply too cruel.
The only thing Muten Natsu could do was find some other way to save Hisana Kuchiki.
Rukia Kuchiki felt a stabbing pain in her chest.
While she was slowly growing closer to her sister, while she was enjoying the privileges of nobility, Muten Natsu was enduring the agony of Hellfire burning through his body, fighting savage battles against Hollows, and forging a Spirit Weapon to save the person he believed wanted to hurt her.
That indescribable despair and pain crossed the span of decades and closed around Rukia Kuchiki's throat.
Because of his Zanpakutō ability, Muten Natsu always gave people a lazy, unhurried impression.
Like a deep pool, so still that not even the slightest ripple could be seen.
But beneath that deep pool, dark currents surged.
And merely sinking into it a little was enough to feel a suffocating weight.
"When I received this Soul Sleep Bracelet, Muten Natsu and I cleared up our misunderstanding." Hisana Kuchiki's expression was complicated. "He told me that since it had only been a misunderstanding, there was no need to tell you."
"You idiot..." Rukia Kuchiki's voice was weak and thick with tears, and they spilled down her face uncontrollably.
Muten Natsu had never changed.
He had always been protecting her.
Just like back in that half-collapsed thatched hut, when he held her tightly and gave all his warmth to her.
The warmth in Muten Natsu's arms always made Rukia Kuchiki feel, for a moment, as though the world itself were warm.
But the world had always been that same half-collapsed hut.
It was never the wind and snow that were warm.
It was his embrace within them.
"You already know most of what happened after that." Hisana Kuchiki wiped away her sister's tears. "I always wanted to find a chance to tell you, but..."
When Muten Natsu was still there, Hisana Kuchiki could not bring herself to say it.
And after Muten Natsu had already left Soul Society, she found it even harder to confess the truth to her sister.
To speak of Muten Natsu to Rukia Kuchiki after she had lost him was simply too cruel.
"Most?" Rukia Kuchiki lifted her head, her eyes red. "What else is there?"
"I... don't really want to say it. It would sound like I'm just making excuses for myself and Byakuya Kuchiki."
Rukia Kuchiki shook her head gently.
"That's not true. Nii-sama was seriously injured trying to save Muten Natsu. I understand how you feel too, Onee-san."
"Rukia..." Hisana Kuchiki carefully leaned in and gave her sister a light hug.
Then Rukia wrapped her arms around her tightly.
"In the end, all of this started because of me." Hisana Kuchiki's gaze was gentle. "For nobles, the continuation of the family line is extremely important. But my condition... Because of that, some members of the Kuchiki Clan tried to restart the transplant plan, and that's how you ended up being convicted. In the end, their plan was taken advantage of by Sōsuke Aizen."
Bringing someone with Rukongai blood into a noble house was considered a violation of the rules and a stain on the reputation of the Kuchiki Clan.
When Byakuya Kuchiki first brought Hisana Kuchiki into the clan, he had already broken the rules.
Later, in order to grant Rukia Kuchiki noble status, Byakuya Kuchiki broke the rules once again.
As the price for that, he swore before the graves of his parents that this would be the last time he ever broke the rules.
No matter what happened in the future, he would uphold them.
Because of that oath, he had to become the captain of the Sixth Division and shoulder the responsibilities of the Kuchiki Clan.
Sōsuke Aizen intended to lure Muten Natsu into Soul Society by making Rukia Kuchiki take the blame.
Meanwhile, some members of the Kuchiki Clan planned to execute Rukia Kuchiki and remove her Soul Sleep.
Both sides pushed their plans forward, and everything progressed with unsettling smoothness.
Byakuya Kuchiki knew what the family intended and tried to stop it, but he was overruled in the name of the rules.
Taking advantage of that situation, Sōsuke Aizen ensured that Rukia Kuchiki was sentenced to the Sōkyoku execution.
If the Sōkyoku had been carried out successfully, Rukia Kuchiki would have been burned to ashes, and the transplant plan would naturally have become impossible.
Some within the Kuchiki Clan wanted to stop the execution, but Byakuya Kuchiki rejected them in the name of the rules.
Because Byakuya Kuchiki understood that even if this execution were stopped, the same situation would eventually happen again.
If the clan insisted on rules, then Byakuya Kuchiki himself would become the rules.
In the name of those rules, he fought Muten Natsu with all his strength at the Sōkyoku execution ground at the peak of Seireitei.
As the embodiment of the rules, he was defeated by overwhelming power.
That defeat forced the clan to realize just how fragile rules were in the face of absolute strength, and it completely destroyed their naive belief that they could use rules to threaten someone powerful.
As for Shunsui Kyōraku secretly infiltrating the Shihōin Clan to steal the Tenshiheisō, the Shihōin Clan turning a blind eye to the theft, their lack of any reaction to the disappearance of the Tenshiheisō, and their failure to notice the disturbance when Jūshirō Ukitake released its seal... these kinds of matters outside the rules were things Byakuya Kuchiki had no intention of paying attention to.
Every action Byakuya Kuchiki took was done to uphold the rules.
His defeat meant the defeat of the Kuchiki Clan's rules.
That left the Kuchiki Clan with only two choices.
Either find a stronger head of the family who could defeat Muten Natsu and maintain those rules.
Or put the rules aside and give up the idea of provoking Muten Natsu.
And since they could not find anyone stronger than Byakuya Kuchiki to lead the clan, the only option left was to keep their distance from Muten Natsu and the people around him.
As for the possibility that Muten Natsu might lose...
Byakuya Kuchiki had always addressed Retsu Unohana as a "senior."
["You cannot protect him forever, Captain Unohana."]
So while she could still protect him, she would do everything she could.
...
By the time Rukia Kuchiki finished escorting Hisana Kuchiki back, the sky had already grown completely dark.
The clear night sky was filled with countless stars, each one flickering like the tangled thoughts inside Rukia Kuchiki's mind.
Seireitei. Central 46. Nobility. Rules. Families. Conspiracies. Betrayal.
Things that once seemed simple now revealed countless hidden layers beneath them.
Before this, all of those complicated things had been kept outside her world by a barrier called Muten Natsu.