Mysteries of Old Tokyo is a detective puzzle game in which the work of a historian turns into a real-life investigation. After taking a position as a researcher at a mysterious company searching for rare artifacts, you begin gathering information about Tokyo's past using archival materials, old photographs, maps, books, and other historical sources. Each chapter is dedicated to a specific period or event, gradually revealing the city's multilayered history. The gameplay revolves around analyzing documents and finding connections between disparate facts. Old postcards lead to real-life locations in modern day Tokyo, where you must compare the past and present, study changes in the urban environment, and search for details that can aid in the investigation.