Dreadfully muddled from start to finish. First, it's about a fantastic contest, then about the main characters' friendship, then about love, then about...magical war!?
The problem being that transitions between any of these are handled very badly. The old is dropped or handwaved away to make way for the new, awkwardly jammed into things. A good example is the whole heart-stealing contest idea, which is central to early chapters, but fades away totally before the halfway point, never to re-surface. This may be due to the unfortunate implications of the rules of the contest, which are so horrible I expected them to be part of the plot. Instead, Anno contrives situations to avoid the conflict and then quietly pretends like it was never there at all. Disappointing, as the situation could have easily been used to drive the plot in an interesting direction.
Also has a tendency to feature secondary characters that appear to be important, only to never be used for anything. This is most apparent in the first chapter, where a character gets nearly a whole page to introduce them, only for them to have literally no significance to anything. Why were they even there?
These serious failings are puzzling given Anno’s experience as an author. Is it because this is her first series for young girls? Regardless, the series’ strengths, the good art and the heroine’s characterization (at least in the earlier chapters) end up wasted.