"Three Shinigami dying mysteriously in a row. So Captain judged this investigation to be very dangerous. That's why he decided to go personally to uncover the truth," Toshiro explained.
But Rangiku frowned. "Of course I know that! So we should—"
"So you should wait here even more!" Toshiro interrupted Rangiku.
"Such a big matter always needs someone to investigate," Toshiro continued.
"Then I'll go too. I'm a bit worried if Captain goes alone," Rangiku said.
However, Toshiro objected. "No, Rangiku, you should stay here honestly. Although this doesn't sound pleasant, you should understand deep down: your current strength is far from sufficient. Going would only burden Captain."
Hearing Toshiro, Rangiku fell silent.
Though reluctant to admit it, Rangiku had to acknowledge that while her strength among Lieutenant-level was decent, that was all. It was far inferior to Toshiro and Isshin. If Isshin encountered an insurmountable crisis, even if she were there, it wouldn't help… she'd just be a hindrance.
Actually, Toshiro was somewhat puzzled about Rangiku's strength too.
Logically, at the start of the plot, compared to other Lieutenants, Rangiku had relatively deep experience. But as the plot progressed, Renji, Rukia, and the others broke through one by one, advancing greatly, reaching Captain-level or even beyond. Yet Rangiku remained at Lieutenant-level, with no major progress.
Regarding this, Toshiro had some speculations. Long ago, Aizen, to collect Shinigami-powered souls for creating the Hogyoku, severely injured the young Rangiku. This was why Gin chose to infiltrate Aizen's side, wanting revenge for Rangiku.
Therefore, Toshiro guessed Rangiku's soul might have been injured during that incident, making it difficult to break through to Captain-level.
After all, a Shinigami's strength, Zanpakuto, and such were closely tied to the soul. If the soul suffered severe damage, a Shinigami's strength would have difficulty progressing significantly.
If Toshiro's speculation was correct, then Rangiku becoming a Lieutenant-level Shinigami itself was quite an achievement. But breaking through to Captain-level seemed almost hopeless.
After calming down, Rangiku said to Toshiro, "Toshiro, you're right. If I go, I'd indeed cause trouble for Captain. How about you go instead? I'm still a bit worried if Captain goes alone."
Regarding Toshiro's strength, Rangiku was quite confident. Though she didn't know exactly how strong Toshiro was, in her view, he was at least much stronger than Isshin.
Hearing Rangiku, Toshiro said dismissively, "Rangiku, you underestimate Captain too much. Captain's strength is very high. Even among all Gotei 13's Captains, few could definitely defeat him. So going alone to investigate probably won't cause problems."
Although Toshiro was confident his current strength surpassed Isshin's, he wouldn't look down on Isshin because of that.
As the father of Bleach's protagonist, Kurosaki Ichigo, Isshin's strength definitely wasn't simple.
Back when Toshiro first joined the 10th Division, Isshin's strength was only at the peak of Captain-level. But later, when Toshiro served as commander of the Hueco Mundo Expeditionary Force and campaigned in Hueco Mundo, breaking through to beyond Captain-level in battle, upon returning to the Soul Society, Toshiro accidentally discovered Isshin had also broken through to beyond Captain-level.
Whether it was Kaien's death stimulating him or it being his time to break through, Isshin successfully reached beyond Captain-level.
Now, over a decade later, how much Isshin's strength had progressed, even Toshiro wasn't sure, because Isshin rarely displayed his strength publicly these years.
But one thing was certain: Isshin's strength definitely ranked among the top even among Gotei 13's Captains.
Rangiku said, somewhat surprised, "Really? Captain is that strong?"
To others, as a Gotei 13's Captain, Isshin's strength was undoubtedly high… but that was compared to ordinary Shinigami outside Captains.
Since Isshin always acted unserious, it was hard to believe his strength could compare to other captains.
But Toshiro nodded. "Yeah. In the Soul Society, those stronger than Captain are only Captain-Commander Yamamoto, Captain Unohana, and a few other veteran captains. Others aren't Captain's match—"
Here, Toshiro suddenly realized something and 'swished' up from his chair.
Toshiro suddenly realized he'd overlooked someone! In the Soul Society, besides Unohana and a few veteran Captains, there was another person stronger than beyond Captain-level Isshin!
'Could it be—?!' Toshiro inwardly exclaimed.
'Calculating roughly, the time Isshin leaves the 10th Division might be around this period. Moreover, since Aizen often hunts Shinigami for experiments, whenever Shinigami mysteriously die or disappear, it's mostly related to Aizen. So, could this Narumishi incident be the one causing Isshin to leave the Soul Society and live in seclusion in the Living World?' Toshiro thought to himself.
Although Toshiro read the original manga, by the time he transmigrated, Bleach had been finished for a while. Plus, after so many years, Toshiro only remembered important parts of the original plot, while the rest was just a general recollection.
And Isshin didn't appear too often in the original. So, regarding Isshin's matters, Toshiro only remembered the general idea.
About exactly which year and which incident caused Isshin to leave the Soul Society, Toshiro didn't remember clearly.
But Toshiro remembered this incident seemed related to Aizen's experiments. Moreover, now wasn't too far from the plot's start. So, considering everything, Isshin likely left the Soul Society around this time because of this incident.
"Rangiku, the division's matters are temporarily yours. I'll follow Captain to check the situation!" Toshiro suddenly said.
"Huh?!" Rangiku exclaimed. "Didn't you just say Captain could investigate alone with his strength?"
"True, but I feel uneasy. So, just in case, I'll go check," Toshiro said.
Then, regardless of Rangiku's reaction, Toshiro immediately turned and left.