It's one of those 'explained, but not exactly' like the thing with Rhine Lab people; Mostima shot her superior with her God-given gun, which is a sin for the Laterano (or the Sankta in particular). The affair has something to do with Exu's older sister and it has since become a state secret that not even Exu knows about. Now Mostima has her gun taken from her, a Notarial Hall agent following her 24/7 that will kill her if she misbehaves, and an unknown creature gnawing at her shadow because of her use of her staffs which are implied to be Laterano eldritch artifacts.
