Haru has survived all of her assailants and passed the test designed specifically for her - or has she? It seems that there is one final peril that has decided to know its face.
That danger is, of course, Tokaku herself, who seems to have taken upon itself to unleash her ability to kill now that it resides within her on her one-time friend. All is not as it seems however, as Haru is saved from impending death by... Tokaku? As her friend whisks her away, confusion gives way to a realisation that it was in fact Nio, not Azuma, who was out to kill Haru, as the overseer of the assassination game has turned assassin herself using her own unique ability.
That isn't to say that Azuma doesn't want to kill Haru as well though, and as the two Azuma's battle it out it becomes clear that they both actually have the same ultimate goal, albeit for different reasons. Unlike Nio, Tokakau wants to kill Haru to prove that she isn't under the control of Haru's ability as a Primer, which she sees as the only way to validate both their friendship and her decision to protect Haru - a rather dire way of going about things, but there you go. Ultimately, all's well that ends well however - Haru survives, Azuma finds the truth she's looking for, and the other members of the Black Class all find happiness. Or run around killing nuns, which I guess is pretty much the same thing.
Trying to end a series like Riddle Story of Devil with a montage of the cast living happily ever after (more or less) is a pretty weird decision, as was its twists surrounding Azuma in this final episode, although it worked reasonably well for the most part in truth. Still, that lingering sense of slight dissatisfaction shouldn't detract from a series that initially looked like being a tired "assassin of the week" story without much to keep it afloat, yet somehow managed to find some surprisingly compelling stories to make its setup work well and deliver drama and even some tears with some genuine heart that surpassed its over-the-top characters. Coupled with increasingly assured animation quality to match the growth in its story-telling and a decent soundtrack, Riddle Story of Devil managed to ultimately present itself as a surprisingly well-told tale that was eye catching in both visuals and story, above and beyond (yet still capable of leaning upon) the silly insanity it initially promised.