Once upon a time our heroine, Himemiya Nagisa, remembers meeting and exchanging rings with the ”Prince of the white roses” after accidentally getting separated from her parents during a festival.

Still treasuring and always carrying with her said ring with the white rose she received, she accidentally drops it while onboard the ship heading for where her father lives outside of Japan.

Falling overboard when trying to catch the ring before it drops into the sea, what will await her when she regains consciousness on an unfamiliar island…?

[From Koorin's review]