Nilay said:
Eva, really? Look, do I have to say this?
STANDS. HAVE. NO. RULES. AT. ALL. They all have the same source (a soul) sure, but they have no shared rules.
The only rules a Stand follows is it's own.
That's a false statement and you know it.
First. Speaking generally,
a Stand cannot be acted upon or affected except by another Stand.
Second. Speaking generally,
a Stand rapidly becomes less powerful if it moves beyond its maximum optimum range.
Beyond that, my statement that you quoted has less to do with Stand mechanics and more to do with established Hamon mechanics. Namely, Hamon requires a conductor in order to be used beyond one's own physical reach. That conductor can be water, seemingly any kind of organic matter, or certain kinds of metal. But it can't leap through the air from one conductor to another, it has to make physical contact. Thus, because Hermit Purple is in direct contact with (or, "is a part of") Joseph Joestar's body - and possibly because it takes the form of a thorny vine - he can channel Hamon through it. Star Platinum, however, is not. Therefore, Star Platinum cannot be used as a Hamon conductor.
Or, if you
really want to get nitpicky over it, then I can say that Hermit Purple has the very unique property or "rule" that, for whatever reason, it alone can conduct Hamon.
The point is, I'm effectively invoking Rule Zero* here, and declaring unilaterally that Star Platinum can't use its own Hamon nor be used to channel Jotaro's Hamon.
*Rule Zero: "What the
director GM says, goes, end of discussion. No 'if's, 'and's, or 'but's."