https://ku-search-tarurata.koyeb.app/
This website allows you to search for Kindle Unlimited books on amazon.co.jp.
Previously, it was challenging to find Kindle Unlimited books using Amazon's search function. This led me to create this website. (Now they should have same kind of search feature in amazon...)
Simply enter the name of the book in the search bar, and you'll see the available Kindle Unlimited books.