For those wondering about jaryuu and power, some WN spoilerucation.
The manga seems to be in a future (or a newly written) arc, but the current arc that this one is replacing has some speculation about the nature of the power of the Jaryuu:
It's faith and terror magic. The more people believe in the horrors of the Jaryuu, the stronger 'it' gets. But because our beloved newt is so unsuitable as a vessel, it gets transferred to Reiko instead, or something. AFAWK the dragon has always been like this, for a long time.