A man (Nakamura Shido) comes to Shinogawa Shioriko (Goriki Ayame) and Itsuura Daisuke (Akira), saying he wants to buy a book. In his hand was a book titled “Introduction to Logic” by Vinogradov Kuzmin. The suspicious-looking man, who had written “Masashi SAKAGUCHI” (Masashi SAKAGUCHI) in letters that protruded from the purchase list, left the store, saying he would come back tomorrow.