While all the other gates are made of stone, Kōfuku-mon stands out as the only gate made out of wood. There’s nothing inside now, but in the past there were two government offices-- to the west of the gate was Jishaza, the office managing the shrines and temples, and to the east was Ōkumiza.
Ōkumiza was the office in charge of resolving property disputes and conducting family registry operations such as birth and death certifications. Like modern times, families would need to register when a child was born. In addition to the name and date of birth of the child, the certificate would also include the names of representatives of the father and mother's family, as well as the neighborhood community. In fact, one of the reasons the process was so standardized was to prevent people from illegally registering as part of the “Shizoku” warrior class.
It’s assumed that the area around Kōfuku-mon was a lively area, with officials coming and going regularly. But these days the area is completely empty. This is due to a policy of the castle's restoration team not to restore by speculation any area for which there is no material evidence. To date, nothing has been found that conveys the inside of Kōfuku-mon, which is why it remains the way it is.
