Huh, my dictionary shows it as incorporated foundation, essentially, just a business. Now, I dont read kanji well, and my translation software just makes jibberish of the site you linked, so I will just bow to your greater knowledge.
The change of Japanese law meant that the foundation that runs the Hiroshima Peace Memorial Museum had to undergo the same process as the Aikikai. It has the same legal status as a 'public interest foundation', but I would not quite agree that the Hiroshima Peace Culture Foundation is 'just a business.' There are no shareholders and the object is to break even and not to run at a loss. I suspect that its finances are subject to greater public scrutiny than those of the Aikikai.