^^ Love goes like... may sound dark, but the lyrics are pretty... hot, if you know what I mean
Well, I think that Kuu doesnt have this kind of song cause since she was a kid she pretended to be a singer and touch people's heart and give them that good warm feeling in their hearts, just like her mother used to do, so this totally directioned her lyrics to the other direction, plus, as happiholic said, she hasn't been "traumatized or anything". ayu, on the other hand, wrote her songs to "save herself", like she said once, so she needed to put all that pain out of her heart in her songs, which gave us those dark songs.