Do you have access to the latest source code for your project? That's really the key question here.
I agree with the poster above — when I've done development in the past, the app owner has their own Apple Developer account and invites the developer to join their team. The app should be submitted to App Review through the owner's account, not the developer's.
A couple of other things to be aware of: if the annual Developer Program fee isn't paid and the account lapses, Apple will remove your app from the store. Once that happens, it's much harder to recover, so time is important here.
Also, check any contracts you have with the development company. You may have rights to the source code, which could matter if the company's assets are being handled through bankruptcy proceedings. Without the source code, you'd essentially be starting over from scratch.
The good news is that if you do manage to get the code and set up your own developer account, Apple has an app transfer process in App Store Connect that can move the app from one account to another — so you wouldn't have to lose your existing ratings and reviews.
I'd definitely follow the advice to contact Apple Japan through Contact Us as a first step. Good luck!
Dean Reyburn, iOS/MacOS developer reyburnengineering.com
(上記は英語で書いていますが、ご質問に対するアドバイスです。翻訳ツールをご利用ください。)