I have a certain amount of sympathy given that Japanese immigration features in all of my nightmares.
That said, attempting to cross borders for the purpose of working illegally (sorry, I don't like the law either, but there is no conceivable way that YC does not count as employment) will not endear you to law enforcement. I wish they had been more polite in the course of discovering your true purpose and refusing you entry, but if they hadn't, that would have been a crazy result under US immigration law.
There's better ways to handle one's business and legal affairs tactically, but start with knowing that the US really doesn't have a visa category "People from countries we like, for any purposes whatsoever, no questions."
That said, attempting to cross borders for the purpose of working illegally (sorry, I don't like the law either, but there is no conceivable way that YC does not count as employment) will not endear you to law enforcement. I wish they had been more polite in the course of discovering your true purpose and refusing you entry, but if they hadn't, that would have been a crazy result under US immigration law.
There's better ways to handle one's business and legal affairs tactically, but start with knowing that the US really doesn't have a visa category "People from countries we like, for any purposes whatsoever, no questions."