家鴨の侭 (あひるのまま) literally means “remaining a duck” or “staying just as a duck.” It creates a memorable image in the song: the speaker spreads their wings and dreams of soaring like a swan, even while still being an ordinary duck, suggesting the courage to pursue transformation without denying who you are.
King Gnu's "BOY" is a pep talk for someone who keeps falling short and keeps running anyway. The opening is all sweat and tears, and the singer's answer to that mess is simple: "息を切らした君は" (you, out of breath) "誰より素敵さ" (are lovelier than anyone). Being exhausted is the attractive part here, not something to hide.
The best image is the ugly duckling, flipped. "家鴨の侭で翼を広げて" (spreading your wings while still a duck) "空を舞う白鳥の夢をみる" (dreaming of a swan dancing in the sky). Nobody turns into a swan in this song. You stay a duck and dream big anyway. Days feel like "気の抜けた炭酸みたいに" (like soda gone flat), which is a very specific kind of boredom.
Phrase worth learning: "道草を食って" (dawdling on the way). Literally it means "eating roadside grass", the way a horse stops to graze, and Japanese uses it for wandering off course. The song treats detours as the point: shortcuts are tasteless, so take the long road, wade through the mud, and when it gets hard, "走れ遥か先へ" (run, far ahead). The dirty shoes and footprints are proof you went somewhere.