The friends that are closest to you are those you can relate to the most. You share the same interests, passions, and goals. In fact, these similarities in personality between you and your friends might have been the very reason you had met them in the first place.
The film Harmonie emphasizes this theme. The protagonists Honjou and Makina are seemingly ordinary high school students who can psychologically connect through the interest they share, that being music. The progression of the film shows Honjou slowly understanding the personality of Makina and at times catching a glimpse of Makina's past through music in a somewhat supernatural manner. At second theme is presented later in the film, that being whether thoughts are best kept to oneself or shared with others.
The film Harmonie was able to incorporate many ideas into a mere 25 minutes. Whether some of these ideas were rushed is debatable. The animations were good, and the one song in the film was well incorporated into the progression of the plot. Also, some parts of the anime are intentionally made unclear so that the reader's imagination can fill in the gaps.
I would recommend this anime-the theme and originality of the film is what makes the film enjoyable. For a 25 minute one-episode anime, Harmonie is very well done.