Origin of "Energy Objects"

As mentioned before on magicthegathering.com, kami creatures in the Kamigawa block all have floating "energy objects" in their art, as a visual cue that they belong to the spirit world.

What's the origin of that visual cue? Early in Kamigawa world-building, concept illustrator Ittoku produced this sketch below. Note the floating heads along the right-hand side.

Kamigawa concept sketch by Ittoku

As Brady Dommermuth reports in today's Ask Wizards, that sketch became the inspiration for Myojin of Cleansing Fire and the energy objects in general.