For high-quality digital versions, look for the Taiyo no Uta soundtrack or Yui’s greatest hits collections to ensure you get the best bit-rate available for your MP3 library. Good-Bye Days - Yui - Amazon.com
If you are looking to purchase or download the MP3, it is available through several official platforms:
Yui’s delivery is raw and sincere, perfectly capturing the theme of cherishing fleeting moments.