For foreign investors, it is necessary to issue a notarial certificate of personal information in their notary office. In some countries, it is called a declaration or affidavit, which will guide everyone to prepare.
There are no other requirements, just prepare the purchase funds, and pay a deposit of 10% for the reserved house, and the final payment can be paid before the house is handed over.
If you need a loan, Japanese residents should pay taxes on their income. If you are an overseas investor, you can apply for a loan to buy a house by setting up a Japanese company.