When Takamori Yuuri was a child, he visited the Century Manor, which was owned by his grandfather. Forced to spend the summer there while his parents went away, Yuuri immediately wanted to go home – until he met a kind boy already living there. He teaches Yuuri origami, and promises to write him letters when Yuuri has to leave again.

Now 18 years old, Yuuri finds himself at Century Manor once more. There, he meets his cousins, Fujiwara Yamato and Takamori Asao. As Yuuri slowly adjusts to his new life, he can't help but think Yamato's kindness is nostalgic, and then he finds familiar origami collected in one of the rooms… What memories and feelings will be remembered in this manor?