Fujisako Aiko is a nice but somewhat solitary girl attending the beautiful and isolated Enishida Academy, a boarding school on a lush, walled-off island. One day while wandering through the island's woods, she peeks out from behind some trees to to see two foreign-looking girls around her age in a forest clearing.

One is cold and pretty. Another is cheerful and happy. In spite of their differences, Aiko soon finds out they are sisters from a royal family from another kingdom! Swept up into their luxurious surroundings and their large household of brothers and sisters, she is happy with her new friends. But what is this subtle wrongness she senses from time to time? And how come she feels so drawn to the obsidian eyes of the coldest sister of them all?