Obviously, because the bad guys are after Sixth. This isn't her threat.
Twelfth, Hirasaka Yomotsu, is insane. He thinks he is a super hero.
Gasai dispatches him.
But it's a double cross! With Twelfth gone, the cult is un-hypnotised, and Sixth turns on them.
Gasai pushes Amano out of harms way, but Sixth orders her cultists to gang-rape her while broadcasting it over the loudspeaker to draw him back out.
Even though Gasai is crazy, Amano won't stand for this, and he kills Sixth by darting her diary.