In his Divine Kingdom, Xi Wei watched as Marni tricked the Rotten Bones cultist, giving them the slip and heading for the refugee settlement.
His ball form 'nodded'. The reason he had assigned Leah her quest was naturally because he had discovered (by spying on the cult's meeting) that the cultists were not planning to kill her, but to sacrifice her as a living offering to Rotten Bones.
He could guess Rotten Bones' intention at once: like himself, the evil god would feed on weaker gods to increase its own power.
The System the girl had was not quite important since it was normal for any devout believers to possess divine miracles on their person, and a weakling like Rotten Bones would never be able to find out anything.