The Sculptor mentions that Isshin was the one who severed his arm, to prevent him from becoming Shura. The amputation of the arm seems to be an attempt to “humble” a person, so that they don’t overstep their bounds and become a killing machine. However, it becomes apparent later that this method is actually counterintuitive, as the Sculptor becomes a “vessel” for hatred, transforming him into a demon. Furthermore, the Shinobi Prosthetic that replaces the lost arm allows for even more efficient carnage, which is what allows Sekiro to potentially become Shura. This theme of self-disfigurement was also prevalent in Bloodborne, where people either blinded themselves or double-wrapped their leg following a superstition—one that Gehrman so strongly believed that he amputated his own leg. Likewise, the lack of vision removed fear, and along with it any sense of justice. The belief that wrapping the leg prevented beast blood gave hunters an excuse to continue killing without abandon. As such, Sekiro is the product of Isshin and Dogen’s subconscious effort to create an amoral war machine. But back to the dragon, the reason it’s missing a limb is because it symbolizes the humility that’s supposed to come from imperfection. I also like the other Anon’s statement about the plucked Everblossom branch.