After the Church War, each sky island retained only one model of each mechanical weapon.
After those synthetic humans had stolen the "Fire Opal," God Communication Island was unable to produce another identical one.
No matter how you look at it, those synthetic humans were responsible.
To prevent Russell, an Outer Island special agent hired by Mental Heavy Industry to solve the synthetic human problem, from reaching God Communication Island, they controlled the Fire Opal in advance to shoot him down at sea.
This was also likely to show Mental Heavy Industry that they had the capability to control the Fire Opal.
The Fire Opal could remain invisibly for an extended time, and if it stopped at a high position, it was hardly noticeable. Meanwhile, the synthetic humans could place the Fire Opal above any target they wanted to bomb, silently launching invisible missiles to destroy it.
—This was a threat.