The Summoning of Susano

[Maku]

Crystals are used to summon elemental entities, as the crystals themselves, in many FF games, are elementally focused. In effect, certain beast tribes literally worship a singular element, not really a "god".

Mog King, is well the King. He isn't a summon, but has a "resting period" in another dimension after his time on our plain of existence.

Kami on the other hand, can be literally anything that is considered to be sacred. Rocks, trees, the three regalia as is with Susano'o. These items are in effect given life simply by worship. They are the embodiment of others hopes, wishes, and dreams.

Literally, anything can be turned into a Kami; however, a full blown summoning like this will be rare. These three items were specifically worshiped by an entire people, and it took three of these objects to full summon Susano'o. I don't think we have to worry about a singular random object sprouting a summon anytime soon, but the potential for more combinations of highly worshiped items is very real with the current way they are going about this.