Amazon tends to send different resolution/quality based on the device. In general, I think Kindle e-readers get lower quality compared to the Kindle for Android and Kindle for iOS apps. That said, if you have the latest Kindle for PC version, you should be getting highest quality, too.
Mind, resolution isn't the same across the board either even with the same publisher. Some have higher res, some have lower res and while that disparity is to be expected between older and newer releases, even on new releases, there are discrepancies. This is the situation in the US. Since you mentioned furigana and kanji, I'm guessing you're getting your books from Amazon.co.jp.
If you're interested, here's some further discussion:
https://www.mobileread.com/forums/sh...d.php?t=295611