It's the Taishou Era.
Around spring, almost a year since she started attending Seiryouin, Yatsuse Kotoko hears of a certain rumour.
There is a cherry blossom that blooms once every one hundred years somewhere in Seiryouin named the "Hundred-Year Cherry Blossom". If you make a wish under the tree after it blooms, the spirit of the cherry blossom will grant it... so she hears.
Kotodama user Kotoko's wish...
Her wish is to deliver the late Nishijima's last words to Kusuka. In order fulfill her wish that cannot be granted by kotodama, Kotoko searches for the Hundred-Year Cherry Blossom.
The partner with whom she was paired up with due to a certain incident is now her lover.
Aided by her lover and her companions, will she be able to find the Hundred-Year Cherry Blossom?
What will Kotoko obtain in the season in which the cherry blossom blooms?
Now, the season in which the Hundred-Year Cherry Blossom blooms will begin...
[Translation of the official website's story summary.]