Onmur
Archangel of Nutella.
Actually I have a better idea of how nobody knows what Rionna does. Simply, if Rionna is going somewhere to kill a grief controller, there aren't many if any witnesses left. For a grief controller to become dominant, there can't be tons of magical girls fighting them, trying their crap in Tokyo or even Sendai would get them massively dogpiled.
It'd have to be somewhere like Mitakihara, small magical girl population, isolationist territory holder. A hypothetical grief controller could kill Mami back when she was alone, kill Kyouko who's most likely to find out Mami died at all, then be killed by Rionna. And the new contracts made after the fact wouldn't know a thing about what happened to Mami by the time someone comes knocking.
This works because I assume that Rionna gets her information through magic (be it a shade or a hired magical girl) and only travels somewhere if she's sure the grief controller has beat or subordinated all the locals, because otherwise she'd make a lot of pointless trips.
I'm going by this WoG, really:
Firn said:Now, the thing about Nadia is that she's seen some shit. Rionna isn't a mass murderer, doesn't mass oppress magical girls. The University Group and the Sendai Group, for example, wouldn't even have been blips to Nadia. And Nadia isn't omniscient. She can only know of the big things - Rionna quietly wandering off to execute a magical girl or two here and there? That's not something Nadia might know about unless she hears about it from elsewhere. Keep in mind she doesn't really stay in any given location for long enough to find out about this kind of thing! However, I agree that the implications Nadia left weren't conducive to this current confrontation. That's one of my mistakes. I could have implied Nadia's unreliability in this kind of situation before.
My take from this is simply that Nadia doesn't know, because Riona's murders aren't big enough to catch her attention.