back number usually sing about love from a guy's point of view, but here the narrator sounds like someone holding everything in. It opens with "流れ出た赤い雫" (red drops flowing out) that come "抱きしめられた記憶から" (from the memory of being held). Her verdict on them is blunt: "人様に見せるものじゃないの" (that's not something to show other people). The words she never said have become "もうひとつの私になって" (another version of me), screaming inside her body.
Then the song turns tender. She talks to her own hidden tears: "こんな色になるまで泣いていたんだね" (you were crying until you turned this colour, weren't you), and answers with "綺麗よ" (you're beautiful). The red drops come back blue in the second verse, swallowed whole and sunk "遠くの海の底に沈んで" (to the bottom of the far-off sea) to wait until they turn into a gem. That's the blue amber of the title. Learner tip: 言霊 (kotodama) literally means "word spirit", the old idea that spoken words carry power of their own, which makes the unspoken ones turning into a second self hit harder.
back number is a Japanese rock trio formed in Gunma Prefecture in 2004 by singer and guitarist Iyori Shimizu, with Kazuya Kojima on bass and Hisashi Kurihara on drums.
The band signed to Universal Sigma and made its major-label debut in April 2011 with the single "Hanabira".