Me and Arc were discussing this scan and we came to the conclusion it is most likely talking about the Soul King, basically describing all the main qualities of the character in short. Which is crazy to think about since this was all stated during Chapter 240, which is several hundred chapters before we got any more specific descriptions of the Soul King and his predicament.
Kubo had all of this stuff planned out during the Arrancar Arc; let that sink in.
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In my right hand, the stone that connects the worlds" - This can be interpreted in two different ways. One can be a more literal interpretation, in that the "stone" here is the Hogyoku and the "worlds" being connected here are the racial boundaries being melded together during the process of Hybridization, actualized by the Hogyoku. Or a more metaphorical interpretation, in that the "stone" here is the Soul King, who acts as the "keystone" of the realms, and uses his Right Arm, the Mimihagi, to connect and hold the realms together.
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In my left hand, the sword that binds existence" - This is most likely about Soul King using the Ceremonial Sword to create the worlds and bind them together, which is shown in a flashback during the anime.
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The black-haired shepherd" - This can be interpreted as both a representation of Soul King's physical appearance, alongside his occupation; acting as the lynchpin of the realms, and more specifically, the Cycle of Reincarnation that allows souls to transmigrate between life and death. And also, a play-on-words on the term "Black Sheep", which is someone who is excluded from society or grouping of people, which Soul King technically was as his existence was functionally Omnipotent in comparison to anyone else. He was completely distinct from anyone during that time.
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The chair of the noose" - This is supposed to describe Soul King's current predicament, specifically how he's simultaneously supported by the Crystal, allowing for his continued existence, but also acts as his eternal prison, representing the noose constricting his ability to live freely.
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I strike the Ibis when the clouds gather" - This requires a further explanation than normal because it deals with real life mythological symbolism; Ibis in Egyptian mythology represents Divine Enlightenment and the direct transfer of one's soul into the afterlife, which, when contextualize to Bleach, it could represent the balance of souls created by the Soul King (with the word "strike" here not meaning a forceful, violent action, but rather a deliberate action), which makes sense since Ibis, during ceremonies, are mummified to allow the direct transferal of one's soul into the spiritual world, which is what the Cycle of Reincarnation is, fundamentally. While the "when the clouds gather" is an additional description in the creation of this balance; the Soul King resides in the Reiokyu, which acts as the "Heavenly Realm" that resides above the clouds, and is the birth-place of this Cycle as it houses its creator and balancer.
