𐰙

𐰙	U+10C19, 𐰙 OLD TURKIC LETTER YENISEI AEY

See also: 𐰘

Old Turkic

Two possibilities:

Clauson (1962) suggests that it was derived from Sogdian 𐼊 (y, “yodh”) ultimately from Classical Syriac ܝ (“yodh”).
Clauson (1970) suggests that it was derived from Ancient Greek Ι (I, “iota”) through intermediaries.

𐰙 (y²)

(Yenisei Kyrgyz) A letter of the Old Turkic runic script, representing /j/, used with front vowels.

Clauson, Gerard (1972) “y²”, in The Origin of Turkic Runic Alphabet, London, pages 70 and 75
Clauson, Gerard (1962) Turkish and Mongolian studies‎^[1], London: Royal Asiatic Society, page 80
Tekin, Talât (1968) A Grammar of Orkhon Turkic (Uralic and Altaic Series; 69), Bloomington: Indiana University, →ISBN, page 27