Guarantee of safe shelter
The roof tiles of the East Garden of the Imperial Palace, just like those of many other traditional buildings, have this design molded in the edges of the roof. Ever practical yet symbolistic, the Japanese are wishing to ward off the bane of times now gone: Fire.
Most buildings were wooden until the end of the Shogunates, and few are remaining because they succumbed to fire at one point or another.
The design observed in the round tiles shows Thunder in the center (creator of fire) and Rain around it (destroyer of fire).