The product is a Japanese paperback book titled "Ankokukan no satsujin" by Yukito Ayatsuji. The book, also known as "The Decagon House Murders", is a mystery novel that follows the story of a series of murders that take place in a hotel with a unique octagonal design. With its intriguing plot and Japanese language, readers can enjoy a thrilling and immersive reading experience that keeps them on the edge of their seats until the very end.