Well technically we have seen Zangetsu manifest for everyone to see, Ichigo's hollow... At the end of the first Arc he explains the hollow and him are the same soul. So when Ichigo dies or gets near death Zangetsu pops out and saves him.
As for Zaraki, i would like to refer them to Magnets with the same polarity. They are exactly Ichigo's opposite and their power is strong enough that it repels and is uncontrolable so it would be safe for me to say that because of that Yachiru is able to be seen by everyone, which would be almost unique.
I do not disagree with you at all, except one point, Zaraki hasn't heard his Zanpakuto just yet... the rest is just my own theory![]()
Zangetsu could be perceived by others, temporarily, because of a device that Urahara had conceived of... ~_~
And yes, he has heard the voice of his
And yes, he has heard the voice of his
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