Sometimes words are hard to voice, sometimes even though you want to shout everything out it's hard to find the time and a way to do it.
A mysterious egg curses the main heroine to be unable to speak after some words she said breaks her family apart. Story starts in this very fairy-tale like way. She is unable to speak and yet she is not the only one with unsaid words. Whether it be the untold confession or a frustration that's been building over the situation. All the characters have something they are unable to speak.

The four main characters are chosen to lead the musical. And in this way both the audience and them get to see that maybe if you can't speak the words, you can express them another way. Seeing the mother of the main heroine finally hearing and understanding the uncomfortable words as she is singing is probably the best scene in the movie and a real tearjerker too. There are other great scenes too. I won't spoil the details, but there is real catharsis at seeing the characters finally communicating.

The romance of the movie is maybe a little bit cheesy, but it's done well and you get to experience some surprises, so I enjoyed it.
The best part is probably the music though. I didn't get the references, but as far as I am aware they use some well known Japanese songs for the musical parts and it fits pretty well. As I am a big sucker for musicals it was nice listening to the songs even though I don't speak Japanese.

Overall I enjoyed the movie very much and I give it 9/10.

More info on the movie on MAL