Why isn't Mystia here?
Mystia's the big boss. The boss doesn't her hands dirty. Instead, she sends the Prismriver Ninja Clan to deal with those who tarnish the beauty of the song.
Additionally, canonically, Mystia's songs are meant to confuse and scare humans, which yukkuri songs also accomplish, so I imagine it would be quite hypocritical for her to silence the yukkuris.
abuse is coming..