Okay, okay, I guess I'm starting to understand Shions reasoning a little more. However, it still doesn't improve my opnion of her as a character.
There's something still bothering me though about Shion impersonating Mion. What would she have done if Keichi and Rena had wanted to see the oni tatoo? Why once she had Keichi in the undergroud chambers did the ruse continue? She had planned on killing him right? So, what was the point in that?