Okay, well, I'd have to go with Bleach on this one. And I know people are going to disagree, but I felt Kubo nailed the character writing with zanpakutou being actual extensions of their personality, or their true inner selves.
Like, take the dichotomy of Shikai and Bankai. Shikai is what the Shinigami wants to outwardly appear as, whereas Bankai is their true self. Take Unohana, for example.
Her Shikai was a healing... thing, because she gave up the title of Kenpachi and went into medicine. Her Bankai was a true representation of her love for battle, where it essentially just killed anything in a specific area.
This also applies to Zaraki. His Shikai was this badass battle axe that could essentially cut through anything. His Bankai reverts him into a mindless berserker demon that just eviscerates everything, or basically, his true self.
I like this form of character writing because it shows, but doesn't tell. Kubo doesn't like to handhold his audience, and I felt like it perfectly matched his form of visual storytelling. Again, I know people are going to disagree with me, but it's just how I feel.