Who are the angels and who are the devils?

What if another Shiki came to Sotoba with Sunako? And what would happen if this Shiki was different from others and brought a whole new ending to existence? What would happen if this Shiki was different thanks to her past as Nanako Yuuki/Koide? Read on to see what her presence can do to a village surrounded by the devils sin of death and a life of peace as breakable as glass.