Tantei Jingūji Saburō ~ Mikan no Rupo is a Japanese style adventure game in the detective/mystery genre. It is the 5th game in the Jake Hunter / Tantei Jingūji Saburō series, being released between Toki no Sugiyuku Mama ni... (1990) and Yume no Owari ni (1998). While following the same formula of the previous titles, the game features a "Zapping System", allowing the player to see the story from the perspective of other characters as well as Jingūji. Also featured in this title is car chase and following suspects in the form of 3D mini-games, although these features would rarely be seen again in future releases.
One day, an air mail arrives in Jingūji's office. The sender was a drinking friend of Jingūji's named Ikegami, the package contained a key that seemed to be from a coin locker. As the detective investigates cases of missing persons, drug dealings, and murders, the mystery of the key is gradually revealed. Now the famous detective has to follow the leads left by his friend and avoid the traps cleverly set by his enemies.