In Japan hōkyō-in-type stupas are usually made of stone, but the small stupa introduced in this article was casted in bronze. It is conceivable that it was made as a relic container.
This stupa consists of two casted parts which are the base and core, and the roof. The surfaces of the four sides of the stupa body and the four corners of the roof are decorated with designs of hōju (chintāmani)-type magic jewels. 
Masterpieces of Nara National Museum. Nara National Museum, 1993, p.106, no.82.