Yoruko thinks that the murder her brother committed seven years ago is a secret to only between them. But the sudden appearance of the victim's hairpin as a present during Ryuuichirou's birthday party makes Yoruko wonder if somebody else knows about their dark secret. [Wikipedia](https://ja.wikipedia.org/wiki/%E7%91%A0%E7%92%83%E5%9E%A3%E5%A4%9C%E5%AD%90%E3%81%AE%E9%81%BA%E8%A8%80)