Well, it's true I haven't seen a story where Shiemi managed to summon both twins before. Usually, it's just Rin.

*ponders* I do wonder where the idea could go. Though I'd have to decide what sort of lives the twins have been living. Are they truly full demons? Were they summoned from Gehenna or have they been living in the human realm? Given Yukio's calm, were they possibly trying to be summoned as part of an escape? From Gehenna? From the exorcists? And, whose side are they on? (At the start; we all know I'll have them good guys before I'm done. It's how I roll.)

Augh! So many possibilities!