The first time I saw rain chains (kusari doi) in Japan in temples in Kyoto, I presumed they were lightening conductors to prevent the wooden buildings from catching fire if struck by a bolt of lightening.
It wasn't until I visited the same temples in the rain that I understood that the rain chains serve as gutters to funnel the large downpours to earth in a graceful stream. Rain chains are found in Japanese temples and shrines as well as private homes.
GoodsFromJapan sells a variety of both modern and traditional rain chains made in Japan that make for a pleasing and aesthetic garden accessory.
Guide Books on Tokyo & Japan