The plot is not exactly new: Girl gets magical object and makes herself older to enjoy the adult world. It is nicely done as it is set into a business surrounding with all its pitfalls and challenges. I bet it is even more hillarious if I could understand the Japanese language and the degree of rudeness this girl inadvertently spills out, but I think one does get the main points.
The story is pretty straight forward, there are no real surprises and it is more like a fairytale for teenagers than a captivating movie plot.There are some strange and a bit implausible story twists (and we are talking magic-mirror movie here), but well, strange things happen in fairytales. It's more Coming of age than romance even though there is a Prince Charming.
The acting was a bit over the top at times for my taste, but still okay.
I didnt really pay attention to the music which means it was neither awesome nor dreadful.

All in all it was an okay movie but I will not watch it a second time.