@kaminomikan remember whatever malicious Ranna is suffering from she had it since birth, remember even the beads the monk used even shatter overtime, so it's the same with the mark. She still loves him greatly however the real issue is not that the magic of the mark is fading but Ranna anger itself can override the Mark's magic, so if she's pissed enough even rokudo can't stop her.
Plot Twist (that everyone already expects): The seal power does not work on Ranna because she is not a "bad girl" and she got a liking on the MC because he treated her well instead of like a demon.
@Kuroku
That would not have happened if only Woody had gone straight to the police.
I think it'd be pretty funny if we the readers who initially thought Sachiko was the big bad of the arc passed her aside when it was revealed she's actually trying to reform her daughter for Tendou as the true big bad only for that to lower our guards to the fact that Sachiko is probably actually still the big bad of this arc. Staaaarting to slowly seem that way despite being Rokudou's ally atm.
Plot twist: The seal's power is working less and less on Ranna as she stops being a bad girl, the problem being that her proclivity to violence is the only thing remaining unchanged