On a cold, rainy day, Takayasu's childhood friend Kasumi
was killed by someone. A year has passed since then.
A letter arrives for Takayasu.
Taking this as his cue, he goes to visit the sender — his relative, Hiiragi.

To learn the truth.
For the sake of time that will never return.
Surely, no one will ever hold that gentle umbrella over me again.

Time has been lost.
Because everything has already come to an end.
Yes...

——Like the sound of yesterday's rain.