The plot of the movie, as some other reviewers have posted, was supposedly dampened because everything was blamed on puberty. However, watching the movie and paying attention, you'll realize that like everything else the aliens though, this idea is wrong.
At the beginning of the movie the aliens are about to go home to their planet and Yobi gives a light hearted reply about what she's gonna do when they are gone. As shenanigans happen and one of them winds up in the human village, Yobi sets out to retrieve him. From the start it's obvious Yobi is a very in the moment character. She steals a charm while displaying all tails, almost falls in an enchanted lake, and has shows very little forethought.
When Yobi starts acting strangely, the aliens assume its puberty, and to some extent it might be, however it is not the main drive. Yobi does not spend any part of the film trying to seduce anyone or commit any other puberty related activities. However throughout she does become moodier. See, I don't believe this moodiness has anything to do with puberty and everything to do with the very real current drama in her life. Think about it, her only family is about to leave, a hunter is trying to kill her for no reason, and everyone keeps telling her about how she is suppose to be acting and feeling. No one, not even the aliens asks Yobi what it is she wants, and truly Yobi probably wouldn't know how to answer.
When the teacher tells her about how the rest of the village treats the students she can relate to them because that's how she thinks they would treat her. Also the aliens are fixing there ship again, meaning they will be leaving the moment they can. But with the boy and the class, even if its slightly confused, she thinks she might have a chance to stay there even as a fox.
At the end when Yobi sacrifices her soul, I doubt its completely out of some rushed love but more because she realizes that one, she screwed up, two he has the potential to live a happy life just as he is and three, and more sadly that she does not have that potential.
So especially to the reviewer who stated that Yobi should have been more antagonistic, Why? She didn't start out that way and had no reason for acting as such. Yobi just wanted to be Yobi, which (in my book) makes it a much better story then if she just wanted to steal his soul. Which has never made sense to me accept under certain circumstances. I mean really, who would really think they can be human and live a happy life after knowingly stealing someone else soul in order to get there. That makes so little sense I don't know why it keeps popping up as actual villain motivation, especially when an otherwise very smart villain tries to pull it off.
