A collaboration project with Mr. Nan HAZAMA, a writer and painter. This song was inspired by the the novel he wrote , and he also drew a picture of the jacket image. Matsui and Amy spend a long time together. Matsui is Amy's loved one. The painter Matsui is always a gentleman and cherishes her, but he can't forget his ex-girlfriend in the depths of his heart. His feeling of love will never be rewarded either, because that person is also his best friend's loved one... "Beyond the door" sings Amy's feelings in that ephemeral and beautiful world view.