I'll be honest and say that this was one of the first Gummy songs I heard, except for the mandatory big single from the past that I listened to when I was just starting to write about kpop, and it was this song that really made my jaw drop. If you remember, I gave it a perfect score earlier this year, and said this:
Each part of this song can stand alone - the instrumental, the melody - but put them together and everything just explodes.
Everything does explode. Epic-ly. And you know it's gonna happen by just listening to the start, but when it does happen it catches you by surprise - that's what makes it so damn good. That's not all - Gummy's vocals have the proficiency and practice to follow the dynamics of the song. Even if the vocals are obviously processed here and there, they're powerful when needed, and they lay back when it's time to lay back.
Which is why not anyone can sing the song - you can't just give something like this to your run-of-the-mill solo singer from a small talent agency with absolutely no idea what she's doing, because more than the fact that it deserves to be sung by someone who can actually pull it off, it's pretty hard to sing. Believe me, I've actually tried. I sounded like crap, so obviously I'm not gonna let you guys hear it. But you get the point.
I now repeat - Gummy knows what the hell she's doing, and she knows how to do it damn well. That, put together with a song that's good on it's own, will come out as pure and utter genius.