U+0457 Cyrillic Small Letter Yi

The Wikipedia has the following information about this codepoint:

Yi (Ї ї; italics: Ї ї) is a letter of the Cyrillic script. Yi is derived from the Greek letter iota with diaeresis.

It was the initial variant of the Cyrillic letter Іі, which saw change from two dots to one in 18th century, possibly inspired by similar Latin letter i. Later two variants of the letter separated to become distinct letters in the Ukrainian alphabet.

It is used in the Ukrainian alphabet, the Pannonian Rusyn alphabet, and the Prešov Rusyn alphabet of Slovakia, where it represents the iotated vowel sound /ji/, like the pronunciation of ⟨yea⟩ in "yeast". As the historical variant of the Cyrillic Іі it represented either /i/ (as i in pizza) or /j/ (as y in yen).

In various romanization systems of Ukrainian, ї is represented by Latin letters i or yi (word-initially), yi, ji, or even ï.

It was formerly also used in the Serbian Cyrillic alphabet in the late 1700s and early 1800s, where it represented the sound /j/; in this capacity, it was introduced by Dositej Obradović but eventually replaced with the modern letter ј by Vuk Stefanović Karadžić.

In Ukrainian, the letter was introduced as part of the Zhelekhivka orthography, in Yevhen Zhelekhivsky's Ukrainian–German dictionary (2 volumes, 1885–86).