Like every other journey RP out there, this one should be rather familiar: exploring the regions, training new Pokemon, and facing enemies of all stripes. But the defining feature of this world is a phenomenon common to all Pokemon: Harmonia, the synchronization between human and Pokemon expressed as a melody. A Pokemon's harmonia is its identity, its soul expressed as music; it can only be heard by those who know the very heart and soul of that Pokemon. Normally, harmonia is completely unheard; no one can detect the harmonia of a wild Pokemon. As a trainer spends more and more time with his Pokemon however, developing a powerful bond through friendship and shared experiences, the melody of his Pokemon's harmonia becomes more and more clear to him. It is unknown how complex a Pokemon's harmonia can become; even the Champions, trainers who have developed their bonds with their Pokemon to incredible extents, admit that their Pokemon's harmonia continue to grow and evolve.
While harmonia simply indicates the depth of the bond between human and Pokemon, trainers can use their Pokemon's harmonia to react swifter and more powerfully in the midst of battle. Along with a Pokedex, new trainers are often given an instrument at the start of their journeys. Typically, they are small, portable, and durable. Ocarinas from the Orange Islands are the most popular choice, but those musically-trained trainers often bring their own--instruments ranging from harmonicas to flutes to harps can be used. Instead of having to verbally command their Pokemon, trainers can play their Pokemon's harmonia on their instrument; by playing different variations on the core melody of the harmonia, the trainer can pass commands and ideas to their Pokemon. This ability becomes more potent as a trainer strengthens their bond with their Pokemon; a newly bonded Pokemon and trainer will barely be able to communicate, while a pair together for years may approach a telepathic connection. Interestingly, as a battle continues, the harmonia of those involved begins to resemble each other--battling truly allows trainers and Pokemon to understand each other, creating a greater and even more powerful melody.
While every individual Pokemon's harmonia is unique, some general patterns can be found. The harmonia of Pokemon of the same species tends to be broadly similar; Gyarados are generally loud and aggressive, while starter Pokemon tend to be friendly, simple, and straightforward. Similar sounds can also be found among those of the same type; for instance, flying types have high, soaring melodies, while dark types have subtle, chaotic harmonies in the background. Moreover, though each trainer gains and develops an individual understanding of how to express their Pokemon's harmonia musically, general ideas and concepts can be taught at schools.