For non-businesses, I think one thing that would make donations a lot more attractive is if they could be made to a tax-exempt org (that means I can donate more at the same cost to myself, or donate the same at lower cost). But I get that something like that is hard to set up for someone who is already under water funding-wise. It would be great if there was an umbrella org that could handle this, perhaps for a fee/percentage much lower than what is usually "lost" to taxes.

patio11's comment is about donating vs. paying by a business entity. Something I hadn't considered is that a business (even if it's just a one-person developer who has incorporated) can pay for software tax-free to any org as long as it's an actual business expense, since businesses (at least in the US, and I assume in Japan as well) are taxed on their profits, not on their gross income.

Patrick's issue with donating as a business makes sense: the tax authorities will look at a donation and think it's a part of a tax-avoidance scheme, but if the business pays for a license to software (even the payment is essentially a part of a custom license, and the software is also available for free under the same or similar terms), and has that payment documented, it's fine.