Over ten thousand of these small stupas were excavated from the site of the abandoned temple Chishakuji at the foot of Mount Senjō in Tottori Prefecture. The surface has been molded into the shape of a Treasure Stupa, and the seed syllable (shuji) for the bodhisattva Jizō (Skt. Kṣitigarbha) appears at the center of each. The Lotus Sutra is inscribed one character at a time at the base of each stupa. 
Object label 

These small-scale pagodas were formed with a mold and reshaped slightly by hand when removed from it. Expressed in relief only on one side, they are of the Jeweled Pagoda type. The Sanskrit seed syllable (Skt. bīja; J. shuji) for the bodhisattva Jizō (Skt. Kṣitigarbha) is modeled into their bodies, and the text of the Lotus Sutra (Skt. Saddharmapuṇḍarīka-sūtra; Ch. Fahua jing; J. Hoke kyō) is incised into their bases one character per pagoda. While this has yet to be determined conclusively, it is speculated that these pagodas represent a form of sutra burial, with a pagoda for each of the tens of thousands of the sutra’s characters interred in the ground.
 
NAKAGAWA AyaEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.346, no.69.