Two spirits combined in one body, the Tsuin Spirits take turns for who is in control of the body, depending on their individual levels of hunger. Hanging out in densely populated cities and invisible to the naked eye, one half sucks the dark energy from depressed people to feed while the other sucks the light energy from happy and excited people to feed. If one side becomes too full off the energy they've collected, they fall below and become dormant until hungry again.