This is a fragment from the head of a bodhisattva statue. One can see part of the floral decoration on its crown. The fragment comes from a statue that was produced by building up red soil mixed with straw and fibers around a wooden core. The details were then modeled on the surface using a fine clay. It is slightly reddened because the statue met with fire at some point in its history.  
Audio guide 

The hint of floral decoration can be seen on the crown of this fragment of a bodhisattva statue’s head. Small pieces of straw were mixed with clay and built up around the statue’s wooden core; refined clay was then coated on and modeled to create the subtleties of its features. At some point, the statue seems to have been in a fire; this is why it is now somewhat red and hardened.
 
NAKAGAWA AyaEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.351, no.16.