Simple.
Calm music helps with respiration.
To be inspired from a talk is something, I suggest you do something a little more serious xD
I like how the artist created the animation frame by frame and I guess he put it in the background and the Inhale/Exhale in the foreground.
He either reduced the opacity or used a lighter color for the characters' animation.
In my opinion it would be best to focus on the concept of breathing so it needs to be darker that way players are not distracted by minor details like this.
Also after the song is over it does not loop back, it just stops.Something that bugged me was how the animation started for quick strokes on the spacebar, i'm sure you noticed.Maybe set in individual sets of animation for multiple keystrokes?
Also you could add in a timer that counts down along with a counter for successful breaths, and if the conditions are met then you can unlock achievements and awards or something like just to keep em going.
Well done on your game and Good Luck !