WARNING: The following contains spoilers for BLEACH: Thousand-Year Blood War, Episode 2, "Peace From Shadows", now streaming on Hulu and Disney+.
In the second episode of the currently-airing second cours of BLEACH: Thousand-Year Blood War Part 2 – The Separation, the Quincies launch their second ambush upon the Seireitei. This time, the Sternritters who plundered Bankai from the Shinigami Captains return to fulfill Yhwach's orders: leave no one alive.
With the Quincies emerging from the shadows once more, the second episode's title "Peace From Shadows" is a hint at one of the episode's most important developments regarding the Quincies – how they survived extermination at the hands of the Shinigami.
The Fundamental Difference
The biggest reason for the conflict between Shinigami and Quincies, at least from the perspective of the Shinigami, is that the Quincies bring about a collapse of the fundamental mechanism of the BLEACH reality – the journey of souls. As Rukia first explained to Ichigo in the first episode of the series, the Shinigami are psychopomps responsible for safely guiding the souls of the dead from the World of the Living to the afterlife: Soul Society. Part of this responsibility involves eliminating Hollows – formerly human souls that have been lost their hearts and become malignant entities that feed on other souls. In eliminating Hollows with their Zanpakutō, the Shinigami purify the corrupted soul and enable its safe passage into Soul Society, where it will be reborn and reside before being reincarnated. This system is delicate, and is a Medici-esque matrix that requires balance on both sides – the World of the Living, and the afterlife. The Quincy means of Hollow resistance involves the complete destruction of that soul, breaking the balance.
The title "BLEACH" is in part a reference to the process of cleansing that Shinigami perform upon Hollows ("harai"), which is likened to using the eponymous cleansing product; however, the Shinigami themselves in their role as Death are still largely associated with darkness and the colour black due to their trademark "shihakushō" ("Garment of Dead Souls"). On the other hand, Quincies also invoke the same image of bleach, but perhaps they emphasize its corrosive qualities, rather than its cleansing abilities; which are two sides of the same coin. The white that the Quincies wear serves the same function as that worn by the Espada; it is a visual communication of their opposition to the Shinigami. There is also the constant paradoxical invocation of the colours black and white throughout BLEACH – while associated with light, and the colour white, the Quincies found strength in the shadows; White, the experimental Hollow that attacked Masaki Kurosaki was actually black in colour.
Enemies Closer
The sealed King of the Quincy. Over 900 years, he shall recover his heartbeat. Over 90 years, he shall recover his intellect. Over 9 years, he shall recover his power. And over 9 days, he shall recover the world. Let us go forth. Uryū. Haschwalth. These 9 days will be the end of this world.
– Yhwach
The Wandenreich, otherwise known as "The Invisible Empire" is the hidden kingdom created within the boundaries of the Seireitei after the Shinigami defeated the Quincies 1000 years prior to the events of the series. The Quincies fled to the place they thought would be the least guarded – the Seireitei, where they used Reishi to create an entire empire within the very shadows of the Soul Society. This new dimension is referred to as the Schatten Bereich ("Shadow Area"), and within this realm is Silbern, the main headquarters of the Wandenreich during the war. As entities that manipulate Reishi from their surroundings, the Quincies used the abundance of Reishi in Soul Society to slowly build their forces in preparation for their retaliation against the Shinigami. As the Quincy legend goes, the King of the Quincies would take 900 years to regain his heartbeat, 90 years to regain reason, 9 years to regain his power, a development that was the very reason for the Auswählen; and, in the last nine days, he will regain the world.
Due to the fact that this Schatten Bereich resides within the Seireitei, the Quincy forces did not need to breach the outer wall of the Seireitei to launch their attack. In this current cours of BLEACH: Thousand-Year Blood War, the environment has a particularly unnatural feel to it with the bright red skies and icy architecture, due to the fact that the Quincies launched this second ambush after forcing the Seireitei to overlap with the Wandenreich temporarily. This detail is particularly important (and is represented by the flipping dominoes in the opening sequence), especially when considering that time moves differently in the Schatten Bereich, and what both Nakk Le Vaar and Haschwalth told their respective opponents: no matter what they have up their sleeves, everything is according to Yhwach's plan.