You'd think that when she hits high notes they come out shrill, but they actually come out quite soothing. That's what her voice is - soothing. It's super smooth, but with the body of a voice with a much deeper timbre.
So the song. To be honest with you, it's quite difficult to choose a repertoire for Hwayobi, if you don't know what you're doing. You can't just give Hwayobi a run-of-the-mill kpop ballad, nor can you shove a repetitive, autotuned, uptempo into her face - that's just not the way her voice works. To be honest with you, whoever does her A&R (if she doesn't do it herself) is rather good.
Ssso What is something I'd have no problem grooving to - it's nice and laid-back with a bare arrangement for pop standards, but it has enough intensity and dynamics running around to make everyone happy. The hook is interesting, and veryyyyyy catchy, the way a lot of people like it.
And it's for that reason that this song is on the list - it satisfies a lot of different groups of people. It fits Hwayobi's interesting voice, it has enough musicality to appeal to the critics like me, it's Hwayobi enough for her fans to but it has a hook catchy and familiar enough to stick to the minds of the masses. Technically, pop music only fulfills either the first or the last 2, sometimes together, but hardly ever is the second characteristic added to the already-full list and when it is, that's a rather rare occurrence. It happens, but not everyday. In kpop.