Why is the camera the weapon in Fatal Frame?
The Camera Obscura feels inevitable now, the signature of the whole series. It was a late invention. In the earliest discussions between director Makoto Shibata and producer Keisuke Kikuchi, there was no camera at all: ghosts were to be avoided, and repelled by light. You would survive Himuro Mansion the way you survive a haunted house, by keeping away.
The team changed its mind on a design principle: the player needed an offensive power, something to fight back with. What they built to fill that space was the camera, and the choice of object did the rest of the design work by itself. A camera makes you stop. It makes you aim. Above all it makes you look, in first person, through a viewfinder, at the thing every instinct says to run from. Kikuchi was opposed to the idea at first; as development progressed he came around, seeing how well it fitted the game's context. The prop itself was modelled on a German military camera.
The combat system then grew around the act of photography. Film is ammunition, in grades from weak Type-14 to rare Type-90. Holding a ghost in the frame charges the shot. The closer the ghost gets, the more damage a photograph does, so the game pays you, in points and power, for waiting until the last possible moment. The most damaging shot in the sequel has a name that became the series' name in the West: the Fatal Frame, fired inside the split second of a ghost's own attack.
So the camera is the weapon for a practical reason and a poetic one. Practically, it was the offensive power the design was missing. Poetically, it turned the oldest horror rule, do not look, into the only way to fight.