The Most Significant Losses of the Thousand-Year Blood War
This arc features the confrontation between the Soul Society and the Quincy Empire, which until then had remained hidden. This is the final battle of a war that began five hundred years ago.
As expected in a conflict of this magnitude, many significant losses occur on both sides, surpassing what was seen in previous arcs.
Chōjirō Sasakibe

As the lieutenant of the First Division, Chōjirō is a character many overlooked and may not remember, as his appearances were not as prominent as others. However, his death is both surprising and significant, as it prompts Yamamoto to act personally when the Quincy invade the Soul Society, almost like a personal challenge.
In a way, his death also marks the beginning of the final battle between the Shinigami and the Quincy.
Genryūsai Yamamoto

We rarely had the chance to see Captain Yamamoto fight, as he usually played a strategic leadership role. However, having participated in the war against the Quincy from its inception, he took this resurgence personally. Thus, he decides to return to action to confront Yhwach, with the goal of ending a war that threatened to rekindle. Loved by many and hated by others, Yamamoto was a character of great relevance and strength.
He tried to correct the past and protect his own, but he did not achieve his goal, losing his life after unleashing his powerful bankai.
His death is not only shocking because he was the captain of the First Squad, someone of considerable strength, but it is also very significant. Especially because of how it affects his closest disciples, Jūshirō Ukitake and Shunsui Kyōraku, the latter of whom, after the tragic deaths that had already scarred him in the past, must face this loss by assuming the position of Captain-Commander and inheriting the responsibility of protecting the Soul Society, as his predecessor wished.
Retsu Unohana

Retsu Unohana always appeared as a calm, kind, and even peaceful person, whom it was difficult to imagine in a confrontation. This image fit perfectly with her position as captain of the Fourth Division, the medical squad.
However, her true identity was very different. Formerly known as Yachiru Unohana, a Kenpachi, she was a feared assassin who earned her reputation for her insatiable bloodlust. This duality explains why everyone, including other captains, showed respect or even a certain apprehension towards this “peaceful doctor,” something that seemed to foreshadow a past to be revealed.
Long ago, her confrontation with a young Kenpachi Zaraki led her to discover her own bankai, but it also caused Zaraki to suppress part of his power as he enjoyed challenges where his life was at stake. When Shunsui Kyōraku becomes Captain-Commander, he asks her to face Zaraki to unlock the latter's hidden potential at the cost of her own life.
Thus, Unohana dies at the hands of Zaraki in a necessary sacrifice for the cause, officially granting him the title of Kenpachi.
Without a doubt, their confrontation was a battle between comrades who, although once rivals, deeply respected each other and recognized each other as equals. Although her death is tragic, it would mark many changes for Zaraki, and Unohana seems to leave satisfied, seeing that the child who reminded her of the joy of battle is heading towards his full potential.
Jūshirō Ukitake

From the beginning, Jūshirō stands out for his calm and kind attitude, yet surrounded by an aura of mystery. Many of the questions surrounding him find answers in this arc.
Without going into great detail, we can say that Jūshirō knew his time was limited and lived it as a gift, enjoying it to the fullest. For many, the most shocking thing about his death is that some consider it a sacrifice in vain, as it fails to achieve its exact purpose.
Still, theories abound about his fate, and having left without displaying his bankai even once, many fans (myself included) hope that more of his potential will be revealed in the Hell arc.
Jugram Haschwalth

He appears as Yhwach's most loyal follower, and his past explains the devotion that leads him to even confront his best friend or sacrifice his own life. However, his final moments, when he offers to heal Uryū Ishida's wounds and bear the damage himself, reveal a more complex side of his nature. This gesture makes him, in my opinion, a character worthy of being remembered.
Gremmy Thoumeaux

Finally, it is worth mentioning Sternritter V, Gremmy Thoumeaux, who was feared even by his own comrades thanks to his ability, The Vision, which allowed him to alter reality according to his imagination.
Although he initially had absolute confidence in his power, with which he claimed absolute victory just by imagining it, he could not defeat Kenpachi Zaraki, who enjoyed facing seemingly impossible challenges.
This battle was more a clash of wills than physical strength. Zaraki showed that his determination and desire to push beyond his limits surpassed Gremmy's confidence in absolute victory.
The outcome could be attributed to the doubts that arose in Gremmy when he considered that Zaraki's confidence implied his ability to defeat him, which unconsciously led him to imagine his own defeat.
This leaves an implicit moral: trust in yourself, even when others doubt, because that confidence will be what you transmit to others.
His defeat can also be associated with Gremmy focusing on Zaraki's strength, coveting it, instead of focusing on his own strength. This is probably because he envied his opponent's taste for challenges, something that, due to his strategic advantage, he himself had never had the opportunity to experience.
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