So it was all an elaborate plan by Koishi to expose her sister to trauma so they could become the same?
What exactly was Sakuya's trauma, and what happened in the end...?
Hmm, this has a similar premise to Fuuzen Lamp's short story, Shoukei no Ori, which also explores dragons and dragon turtles. Pretty much, Yacchie mistaking Meiling for her lost sister. Good read too.