A fragment of wall from the Kita Ote Turret Gate ruins (北大手櫓門跡, near the present-day location of Kato Shrine) was found to contain a carved image of Kannon Bodhisattva (観音菩薩) of about 40 centimeters in area, depicted surrounded by a halo and riding atop a lotus leaf. According to the Kumamoto Castle Research Center, this is likely the remains of an “itabi” (板碑), a stone monument used as a memorial to ancestors during the Warring States Period, which preceded the Edo Era.
The article notes that stone from a variety of nearby sources was utilized during the rush to build the castle, and that this figure was likely conscripted in the campaign, spending the next 400 years as part of the wall. The Center’s director was quoted as saying, “We came across an artifact allowing a glimpse of an era predating the castle itself.”
There is no word on any search for its original owners. - William
http://www3.nhk.or.jp/news/html/20160513/k10010519781000.html