Maybe it’s because I read it all in one sitting but I liked this story a lot. Kotori, Sotoka, Chika, Shiori, and Hiwa are all interesting characters that have multifaceted personalities, and we get to see each of them interacting with and learning from one another.
Seeing Kotori’s (and to a lesser extent Hiwa’s) development throughout the series as she tries to understand human emotions is really interesting direction to go. Seeing her go from being innocent and pretty much an air head to being a little more aware of her own feelings and struggling with relationships that can’t be mended and jealousy is fascinating to see.
It’s hard to say that any one character is the protagonist, they all just happen to be living in the same time and place and we see them all interact for the short window of time the manga reveals.