This is Aimer's theme for the Entertainment District Arc of Demon Slayer, and it opens like a drumline. Those "da-ta-ra, ta-ra-tat ta" chants are pure rhythm, a war drum before a fight, and they come back between every verse.
The imagery is all night-time colour: indigo dropped onto fabric, a vermilion moon, flowers blooming on someone's sleeve (誰が袖に咲く幻花 [an illusory flower blooming on someone's sleeve]). It fits a story set in a red-light district full of kimono and lanterns. But the core of the song is stubbornness. My favourite line is 選ばれなければ 選べばいい [if you aren't chosen, then just choose], which is a brilliantly blunt answer to being overlooked: stop waiting for permission. Japanese packs that into two verb forms, the conditional -nakereba (if not) and -ba ii (it's fine to, you should just).
The chorus is a shout: 声よ 轟け [voice, roar!]. 轟け is the command form of a verb for thundering or booming, and Aimer uses it to send her voice past the night, toward views once blurred by tears. She doesn't even need to know what she's playing or for whom. Every dark feeling and long struggle gets told 歌と散れ 残響 [scatter with the song, echo], and the title itself is that idea: an echo, scattered as a song. Then there's the challenge 逃げ出すため ここまで来たんじゃないだろ? [you didn't come this far just to run away, right?], with the rough, casual だろ at the end that sounds like a friend shoving you back into the fight.