15 parts Complete Harmony is an average girl, living an average life. She does the same thing every day: attending school, doing homework, eating and then sleeping. She doesn't expect anything out of the ordinary.
Things start changing, however, when her best friend, Kazuki, starts acting weirdly. She has to deal with mood swings, cryptic messages and random disappearances. Every day, he tells her something in a different language. He never tells her what it means, though.
Then one day, he disappears completely and Harmony doesn't know what to do. She needs her best friend back, even if he does come with cryptic messages and mood swings.