Grandmaster Domain

"The power, the flawless technique... No doubt about it. You've arrived at our "territory". So you have indeed set foot onto hallowed ground!"

- Katamori Tachibana speaking to Raian Getsueikirite.

The Grandmaster Domain (団長領域, Danchō Ryōiki; literally "Grand Master Territory") is a status coined by Genryūsai Shigekuni Yamamoto that refers to individuals that have reached the pinnacle of a respective field of combat. In doing so, they have essentially "progressed" beyond the dimension of normal spiritual beings and have obtained an almost transcendent power.

Overview
By figuratively "breaking through" the "Meijin Shell" (名人の莢, Meijin no Saya; literally "Shell/Hull of the Master"), which refers to the supposed limit of Shinigami capabilities as Aizen himself once claimed to exist, one may cross over onto the hallowed ground of the Grandmaster Domain. It is a process that varies between beings and isn't something that can ever be taught. As Seireitou himself has explained, the Domain is not something you "climb up to" but rather something you "fall into". In other words, it is impossible to actually work up toward reaching this territory of skill and it is actually something that happens on its own when the conditions necessary for the ascension have been met.

While this is a status not exclusive to Shinigami only, as even Arrancar and other spiritual beings are capable of attaining the territory, the methods of fighting that are normally referred to when discussing the domain are commonly the Zankensoki: the four fields of combat that Shinigami typically utilize.

Mediums & Expressions
Those who have reached this domain find that the other fields of combat can serve as mediums for their craft. Yamamoto himself had expressed his power over Zanjutsu through two outlets before his death: through the use of Ikkotsu, which is an unarmed version of the, and through Ittō Kasō, a spell of his own presumed creation that takes on the peculiar shape of a katana tip composed of red flames.

Seireitou Kawahiru has also demonstrated similar feats by expressing his Hakuda through the three other fields of Shinigami combat.

Failed Attempts
There are those that have accomplished similar feats and have broken through this proverbial hull by alternate means, such as Sōsuke Aizen using the powers of the Hōgyoku, which allowed him to evolve beyond the two-dimensional status of Shinigami and Hollow. However, despite this, it has been explained that Aizen had trapped himself upon doing so. He had indeed broken through the Meijin Shell, but in doing so in such a roundabout manner, he locked himself in a sort of limbo between the shell and the domain. No matter how strong he would become from this point on, he had reached his limit and would be unable to actually move beyond his status, which soon led to his utter defeat.

Ichigo Kurosaki, upon learning the and achieving a brief moment of Bankai Mastery, was said to have touched upon the outermost layer of the Meijin Shell and was merely a step away from the domain. However, since his fight against Aizen and the subsequent loss of his powers, he has shown no signs of returning to this stage as of yet; even after regaining said lost powers.

Behind the Scenes
The concept behind this was inspired by a similar ranking system found in the manga series History's Strongest Disciple Kenichi.