Board Thread:Questions and Answers/@comment-22798516-20130923164947/@comment-12864920-20130926114758

According to Kageyama's line with Garsha and Vanfeny in the Chrono Stone game, he actually implied that, along with their SSC abilities, mixi max and keshins does not seem strong in his opinion. So I guess that that soul is stronger or a complete version of keshin.

Or either some players of Earth Eleven are incapable of using keshins. So instead of using something that they couldn't use, Kageyama decided to have them use the power that every humans had.