*Warning: May contain vague spoilers*
The general story behind this was very good; however, I felt that things could have been developed much more than they were. We're left to wonder the whys and hows behind Garin's actions. The main character herself isn't allowed to develop properly. After her escape, we're left to wonder what happened in those blank years. She feels the need to hunt down her own brother, but there's no indication that she's been attempting to train herself in her unknown powers or to give herself an edge over her brother, who would obviously be honing his own powers in those years. The introduction of the past Guardians is interesting, but it only serves to confuse things during what you'd expect in the "final boss fight".
The presence of the three college students does little to enrich this story. They know of Mienya's existence and provide for her, but they don't question the possible danger until danger occurs. It's both naive and unrealistic, especially when Mienya's presence is merely that--a presence and nothing that adds to or detracts anything from their lives. She's simply there. The students could have had a larger role in the story, other than those of "provider" and "secret keeper".
Overall, the story was good. Some things should have been explained, such as Garin and his choices. Others should have been developed more, such as the secondary characters and their roles. This book is the first of what looks like a series. It's interesting, but I'm not so willing to continue after this first installment...