Finding my Dad’s bank account

I'm not sure how these things work so I figured you guys might know.

So my parents came to Japan to buy a house (my father's japanese), and they made a bank account and put some money in it for a deposit, when we found a house.

Unfortunately, my father's a bit old and he doesn't remember which bank it was, and doesn't know where any of the cards or forms are. He also doesn't live in Japan, so we can't just pop into random banks to see if he has an account.

How can i find which bank he has the account with?

(His health is also not great, so if he passes, it'll be a sh*t show of figuring out how to get the money back)

Thanks in advance.

tldr:

• Dad made bank account in Japan (doesn't live in japan)
• Lost all the information
• Doesn't remember which bank
• Wants to find out which bank
• I'm in Japan
• wat do