逆夢(さかゆめ) is a poetic Japanese word meaning a dream that comes true in reverse, or whose meaning is opposite to what was seen. It is much more distinctive than the everyday word for “dream,” making it an intriguing entry point into the song.
At the end of Sakayume, the singer wonders whether their love will become reality or remain an inverted dream: 正夢でも 逆夢だとしても (“whether it is a true dream or a reverse dream”).
Sakayume is a love song that keeps arguing with itself. The title is the word in the very last line, "正夢でも 逆夢だとしても" (whether it's a dream that comes true, or a dream that turns out the opposite). In Japanese, a masayume is a dream that comes true and a sakayume is one where the reverse happens, and King Gnu leave it open which kind this love will be. The chorus is a full surrender: "あなたが望むなら" (if you want it), "この胸を射通して" (shoot right through my chest). The singer calls himself "頼りの無い僕" (unreliable me) and hopes that someday he could "何者かに成れたなら" (become someone).
The verses are full of winter. "白い息は頼りなく" (my white breath, so weak) melts into the cold, and the warmth left over from holding hands is "あまりに頼りないの" (far too little to rely on). He remembers a time when he assumed spring, and the person beside him, would always just be there: "そう思っていたあの頃" (back when I thought so). Then it gets dark in a way I love. He admits "この愛が例え呪いのように" (even if this love, like a curse) eats into his body "じんわりとじんわりと" (slowly, slowly), he wants it anyway. Learner tip: じんわり is a soft sound word for something seeping in gradually, like warmth or pain. It is a heavy song, a bit much in places, and that is the point.