The Cursed Seal fundamentally reshapes his entire worldview, which is the most interesting part of his arc for me. We meet him as this rigid fatalist, convinced destiny is written at birth because of the branch family seal, and he wields that bitterness like a weapon against Hinata. His development isn't just about getting stronger to beat people; it's about unraveling that internalized dogma. The seal is the physical proof of his 'fate', so when he starts questioning its meaning—especially after Naruto's whole deal—his character actually grows.
Seeing him go from using the seal's power out of hatred to, eventually, sacrificing himself to protect others without a second thought? That's the full-circle moment. The mark never goes away, but what it symbolizes to him completely changes. It stops being a chain and becomes, weirdly, part of his identity as a protector. His end isn't about being free from the seal, but being free from the idea it controlled him.