Modi Letter Vocalic Rr

It marks long syllabic r, transliterated ṝ.

It is a vowel, not Modi ra 𑘨. Modi and Devanagari are Nagari scripts.

How did Modi writing change?

For fast administrative writing.

Modi dates to the fifteenth century; its oldest surviving document is from the early seventeenth century. Origin stories credit Yadava minister Hemadri Pandit with bringing it from Sri Lanka, or Shivaji’s secretary Balaji Avaji with creating it; both are uncertain.

Marathas adopted Modi for administration in the seventeenth century. It served letters and revenue records; Balbodh, a Devanagari style, served literary and sacred texts. A Peshava-office letter survives from 1721. In the nineteenth century, print favored Balbodh; Modi ended in the 1950s.