While modern science cannot explain the origin of humans and Pokemon alike, it is a commonly accepted fact that the two share a special bond with one and other. Legends tell that humans and Pokemon are two sides to the same coin. Just as the True Legendaries and even the Creator had ambitions, emotions, diversity and power, their creations reflect this. Pokemon inherited their types, many forms and phenomenal powers from the raw forces that forged our universe. Humans were born of the emotions, ambitions and will that drove them forward. Because of this relationship, a special bond has always existed between Human and Pokemon.
When Human and Pokemon train together, they develop a spiritual bond with one and other. When this bond becomes strong enough, the two halves can finally unite once more, forming what we know as a Fusion today. It is important to note that despite this mystic bond, extreme physical or emotional trauma can prevent a human or Pokemon from using properly. In such cases, the body of the victim will refuse any new fusions until the subject recovers, if ever. Although rare, it is possible for this to happen to Fusions as well. Fusions who endure extreme trauma may lose their ability to change their form, or fuse with new Pokemon.