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Kickstarter is an organization that gets people to pledge money for a project, and if the funding goal is reached, the person that requested the funding gets the funding. It is an all or nothing situation. If people pledge 100% or more of the amount requested, you get the money. People expect something - a copy of a book, tickets to a movie premier, something related to the project - in exchange for their pledge.
The reason that Kickstarter requires a SSN is so that they can report the payments on a Form 1099-MISC to you (or your US relative). This would be considered US-Sourced income, so there are no foreign tax credits that you, living in China, could use to offset the US tax on this income. Your US relative could turn around and pay the money to you or your company, and report the payment on another Form 1099-MISC, but then you would pay the tax on the income. In short, SOMEONE has to pay the tax!
The IRS defines gross income as all income you receive in the form of money, goods, property, and services that is not exempt from tax. You are receiving money from a fundraising company in support of your developing an invention. This falls within the definition of gross income.
In answer to your question, yes, your US relative would be taxable on the earnings. If the relative paid it to your LLC, your US relative would get a deduction for the amounts paid, and the LLC would be taxable on the income. If Mr. A, your relative, does not pay the money to you, he would pay tax at a rate of 15.3% for Self-Employment tax, PLUS tax at whatever his marginal tax bracket is, plus state tax at whatever marginal tax bracket he is in. For example, if he were in the 25% Federal marginal tax bracket, he would pay 15.3% + 25%, or 40.3% tax on the income. He would also pay state tax on the earnings, as I said.
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