Hueco Mundo, Las Noches.
Although Grimmjow and the others tried to keep a low profile when leaving Hueco Mundo for the Living World, they were ultimately discovered. Or rather, Grimmjow's every move was always within Aizen's expectations.
Even the very act of Grimmjow and the others going to the Living World without permission was a result Aizen deliberately allowed.
Nevertheless, Aizen still pretended to discover it some time after Grimmjow and the others left, and expressed his 'dissatisfaction' with the matter.
Thus, Aizen's most loyal subordinate, Tosen, volunteered to go to the Living World to bring back Grimmjow and then punish him.
"Aizen-sama, Grimmjow is far too presumptuous! He has no respect for you at all! Please allow me to go to the Living World, bring him back to Las Noches, and administer severe punishment!"
Tosen said indignantly.
"Go to the Living World to bring him back?"
Aizen pondered for a moment, then agreed, "Very well, I leave it to you, Kaname."
"Aizen-sama!"
At that moment, the Tres Espada, Tier Harribel suddenly walked in from outside the throne room.
"Aizen-sama, please allow me to go together with Tosen!"
Harribel requested.
"Oh? Harribel, you've come as well? But you volunteering is quite rare."
Aizen said with interest.
"Aizen-sama, forgive my presumption, but Hitsugaya Toshiro of the Gotei 13 is currently in the Living World. If Tosen goes alone, should Hitsugaya Toshiro intervene, not only would he fail to bring back Grimmjow, but Tosen himself might not be able to return safely to Hueco Mundo. Therefore, please allow me to go with Tosen. That way, even if we encounter Hitsugaya Toshiro, my strength should allow everyone to return safely to Las Noches."
Harribel explained.
"I see, so that's it, Harribel. I am very pleased that you have such a sense of camaraderie."
Aizen said with a gentle smile, seemingly fully believing Harribel's words.
"Since you are willing, Harribel, you may go with Tosen."
Aizen agreed.
"Yes! Aizen-sama!"
Harribel exclaimed loudly.
…
Outside the throne room.
Harribel and Tosen, ordered by Aizen to go to the Living World, were walking side by side on their way out of the palace.
"Tosen, I apologize. My reason for wanting to come along is not because I underestimate your strength..."
"I know!"
Just as Harribel was about to explain that she didn't look down on Tosen's abilities, Tosen interrupted her.
"I know my strength is not great. Even compared to some of the lower-ranked Espada, I might not have any clear advantage. So your concern is entirely correct."
"In fact, I am quite pleased that you volunteered to come to the Living World. Most Espada are unruly, but your willingness to share Aizen-sama's burden shows your loyalty to him."
Tosen greatly appreciated Harribel's initiative to accompany him to the Living World.
In Tosen's view, the scenario Harribel worried about was very likely, given that Toshiro was in the Living World, and their arrival would indeed risk encountering him. Harribel choosing to step forward despite the danger of facing Toshiro and go with him to the Living World was a testament to her loyalty to Aizen! And anyone loyal to Aizen was a comrade to Tosen Kaname.
Seeing that Tosen unexpectedly held her in high regard, Harribel decided not to stand on ceremony and proactively asked about something that had been on her mind.
"Tosen, you and Aizen-sama were Captains in Soul Society for a long time. You must know Hitsugaya Toshiro, one of the fellow Gotei 13 Captains, quite well. Can you tell me about him?"
Harribel asked nonchalantly.
Tosen, not overthinking her request… after all, they might encounter Hitsugaya Toshiro on this trip, so Harribel seeking information about their potential 'enemy' was perfectly natural… spoke to Harribel about Toshiro without any guard.
"Hitsugaya Toshiro is the most prodigious Shinigami in Soul Society's history and the greatest threat to Aizen-sama..."
As Tosen spoke, Harribel grew increasingly certain about a suspicion she held.
Her reason for volunteering to go with Tosen to retrieve Grimmjow was, of course, not out of loyalty.
Although she defied Aizen's orders less often than other unruly Espada, which might be considered relatively 'loyal', it still wasn't enough motivation for her, typically uninvolved, to volunteer for the Living World.
Harribel's primary reason for insisting on going with Tosen was to determine if 'Hitsugaya Toshiro' was the same 'Hitsugaya Toshiro' who had saved her and her companions all those years ago.
Inside the throne room.
After Tosen and Harribel left, Aizen, now alone, suddenly smiled inexplicably.
"Harribel... Hitsugaya Toshiro... Heh... How amusing..."
…
Living World, Karakura Town.
Boom!
Toshiro unleashed an ice-blue Kenatsu that shattered Shawlong Koufang's Cero.
"Shunkuho!"
Toshiro's figure flickered, instantly closing in on Shawlong Koufang.
"Way of the Sword: Severing!"
Toshiro gripped his sword with both hands, channeling his full power into the Zanpakuto, and brought it down upon Shawlong Koufang's head with lightning force!
Shawlong Koufang quickly crossed the ten-fingered blades of his left and right hands in front of him, trying to block Toshiro's attack.
Shrrrk—!
The sharp Zanpakuto cut through Shawlong Koufang's claw blades with unstoppable force, continuing its descent towards his head without pause!
Squelch!
Unsurprisingly, Shawlong Koufang was cleaved in two by Toshiro.
Thud!
Shawlong Koufang's lifeless body fell from the sky, crashing onto the ground below.
"Phew..."
Toshiro exhaled deeply, looking at the fallen corpse, and said with a hint of admiration, "What a tenacious fellow..."
Although the gap in power between Toshiro and Shawlong Koufang was vast, and it wouldn't have been strange for Toshiro to instantly kill him, the reality was that it took Toshiro considerable time and effort.
This wasn't because Shawlong Koufang was particularly strong… in fact, his strength was comparable to an early-stage Captain-level Shinigami, weaker than any Gotei 13 Captain. The main reasons Toshiro struggled were because he hadn't released his Zanpakuto and because of the [Spirit Restriction Seal].
To prevent Captain and Lieutenant-class Shinigamis from affecting the Living World's souls, they are implanted with the Spirit Restriction Seal, modeled after their respective division insignias, into a part of their body before coming to the Living World. Once the Spirit Restriction Seal is implanted, the Shinigami's Reiatsu is restricted to one-5th of its original power. So even for someone of Toshiro's caliber, having only one-5th of his power and not releasing his Zanpakuto made killing a high-level early-Captain-class opponent no easy task.