The song was written specifically for Midnight Sun to reflect the story of Kaoru Amane, a girl with a rare skin condition (XP) that prevents her from going out in the sun.
It became YUI’s highest-selling single, with over 200,000 copies sold . Its popularity significantly boosted her subsequent releases, such as "I Remember You". Good-bye Days - YUI
is the fifth single by Japanese singer-songwriter YUI , released on June 14, 2006, under the artist name "YUI for Kaoru Amane" . The song served as the theme for the film Midnight Sun ( Taiyou no Uta ), in which YUI also made her acting debut as the lead character. Production and Release The song was written specifically for Midnight Sun