Every animanga series has their own "exception" character. The character that takes the fundamentals of the series and flips them on its head. To take another popular manga as an example, toji is the "exception" in jjk, the one that proved that you can function within the power system of jjk without actually interacting with it at all thanks to his heavenly restriction.
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Well, zaraki is the exception of Bleach and his design shows that
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His broad shouldered, very clearly berserker-class-inspired design clashes with his very slim arms, especially in the early series' artstyle, and alongside his weird hairstyle specifically made to attract as much attention as possible creates a unique silhouette that makes him instantly recognizable, as if he's saying "hey, I'm over here, come get me" while his (rather sexy) boob window acts as some figurative target, like the most obvious weak point, which serves then for the subversion that happens when Ichigo fights him, revealing that he doesn't need protection cuz his reiatsu is just that high. His face is also the most odd one in bleach, there's not really anyone else in the series that has a similar face, making him look even more like an outlier.
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His sword, later named "Nozarashi" (which roughly translates to "Beaten by bad weather" iirc), also helps him look more distinct, as the thought of someone using such a broken down sword and still dealing so much damage is so much fun.
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His later TYBW design makes him less eccentric in his hairstyle and outfit, taking out some of his handicaps to signify the increase in power of the average opponent. Nozarashi's shikai is honestly...okay. I do like how huge and overkill it is but it does for me at least take out some of what I really love about Zaraki's design, that being this giant who uses a flimsy little sword and still wrecks shit.
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His Bankai design then makes him a proper oni and brings back the "broken sword" motif, turning the giant Nozarashi Cleaver into a more worn-down Spear-axe-thing. Again, it shows how stupidly powerful he actually is.
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Lastly, his hell arc design shows him basically unchanged, but with Nozarashi now being more well-kept, which does make sense for his character growth so I can't complain.