From what I hear, banks in the states tend not to lend to people living outside the US unless they have tons or easy to collect collateral (like loads of stock on NYSE or a house somewhere in the US they can get their thumbs into). If you are based all in Japan, they will not think too highly of you - what you are asking for is a morgage, and banks like to be able to repossess and resell defaulter's homes, something they would have trouble doing if you only have assets in Japan.
Japanese banks might lend to you, but you are auotmatically a high-risk loan. You are a flight risk. It doesn't really matter that you have roots in Japan, are married to a Japanese lady and have a good job. You could still run easily to another country with all that cash and the bank would never see a red yen of it back.
Your ray of hope is that I have heard of foreigners being sponsored for loans by a Japanese citizen who does have collateral - ie your wife's family, a friend, or even your wife is she has any considerable assets in her name. While your wife might not be able to get a loan, she might be able to sponsor you to get a loan. You might have to go down to various banks in person and together to convince them you are serious, but you will probably find someone who will play ball. But expect to go through a lot of false starts. They probably don't have a lot of couples like you come in the door, so turn on the charm, the keigo, and see what comes of it.
Good luck!
