Why Sternritters can't stay outside of the Shadow Realm for an extensive period in Bleach, explained

The Wandenreich army’s elite group of Quincies, known as Sternritter in Bleach, is a formidable antagonist organization introduced in the Thousand-Year Blood War arc after the Fullbringers. During the first invasion of Seireitei, these individuals were powerful enough to rampage through captain-level shinigami without breaking a sweat.

After killing Yamamoto, Yhwach could have continued his battle with Ichigo and let his Sternritters destroy the remaining shinigami. However, he and his subordinates called off the fight and retreated to Wandenreich (the Invisible Empire) after their shadows appeared automatically.

Despite possessing dominant feats, these individuals can’t stay outside the Schatten Bereich or Shadow Realm, and there is a reason behind it, which will be explained in this article.

Disclaimer: This article contains heavy anime and manga spoilers for Bleach.

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Why do Sternritters have a time limit outside the Shadow Realm in Bleach?

Unlike Hueco Mundo and Soul Society, Quincies Shadow Realm exists within the dimension of Seireitei. The only place that acts as a living heart of the Shadow Realm is a large ice-encrusted palace called the Silbern, the headquarters of Quincies located within the Wandenreich. Silbern is as large as the entire Seireitei.

The absence of a considerable number of Quincies, including Yhwach, for more than a certain period outside the Silbern, will eventually destabilize the building, causing the Shadow realm to merge with the Seireitei. Besides Mimihagi (Soul King’s right hand), Perninda Parnkgjas (Soul King’s left hand), and Gerard Valkyrie (Soul King’s heart), the rest of the Sternritters received dominant powers through Yhwach's blood.

The Sternritters, the most potent and advanced generation of the Quincies, possess an immense reserve of Reishi, which channels throughout the Silbern and sustains the Shadow Realm’s dimension. During his fight with Ichigo, an automatic portal manifested in front of Yhwach, after which Yhwach’s chief advisor, Jugram Haschwalth, revealed they had exceeded their time limit working out of the Shadow Realm.

Yhwach believed he and his troops still had time but eventually realized that Sosuke Aizen had dulled his senses during their meeting. Along with Yhwach, his entire Wandenreich army, including his Sternritters and the Soldats, returned to Wandenreich once to balance the Reishi flow within Silbern.

In Bleach, before Wandenreich, Yhwach founded the first Kingdom of Quincies in the human world, Lichtreich (Star Empire), over 1000 years ago. In the span of 200 years after his birth, Yhwach managed to extend Lichtreich to all nearby countries, mainly by conquering the northern lands.

After the first generation of Gotei 13 captains brutally slaughtered most of the Quincies, the remaining members, including Yhwach, escaped from the living world to Seireitei, believing it to be the most unguarded place.

Due to the abundant amount of Reishi in the surrounding area, the members created the Shadow Realm, a parasitic dimension that would keep feeding on Seireitei without alerting the shinigami’s senses. In the upcoming Bleach: Thousand-Year of Blood War episodes, Yhwach would eventually fuse Silbern and the entire Wandenreich empire with Seireitei to bypass the time constraint.

Yhwach waited for over a thousand years, reestablishing his fallen empire, gathering enormous amounts of Reishi, and building a whole new generation of Quincies who could easily rival the new Gotei 13 captains. After the first invasion, Yhwach weakened the willpower of the Soul Society by defeating Yamamoto Genryusai Shigekuni.

The Wandenreich army never really breached the impenetrable Pure Soul Walls in Bleach: The Thousand-Year Blood War, as they existed within the radius of Seireitei. During the first invasion, Yhwach and his Sternritters utilized a considerable amount of Reishi. They will return to Soul Society once again after replenishing their reserves.