Brook and co. will soon free and ask Gunko the questions
Another flashback in this arc incoming
IMU / Gunko could be explained
There could be an ancient prophecy regarding the final war involving a "musician" from the bloodline playing some role.
Esperia kingdom could have ties with Davy clan.
IMU perhaps wanted to hijack prophecy
What happened to Candelle was to give shape to that.
By destroying the nation and taking Gunk, the World Government successfully severed her from her lineage.
Gunko now carries Esperia's heritage and the genetic lineage of a prominent World Noble/God's Knight family - a perfect vessel for IMU