Where does “я” come from?

я (Mongolian) comes from Russian я, from Old Church Slavonic ꙗзъ, from Proto-Slavic (j)azъ, from Proto-Balto-Slavic ēź-, from Proto-Indo-European éǵh₂ — I.

Ancestry of “я”, step by step

Step	Language	Word	Meaning
1	Russian	я	I first-person singular subject pronoun
2	Old Church Slavonic	ꙗзъ	—
3	Proto-Slavic	(j)azъ	I
4	Proto-Balto-Slavic	ēź-	—
5	Proto-Indo-European	éǵh₂	I

Every word from Proto-Indo-European éǵh₂ →Every word from Proto-Balto-Slavic ēź- →Every word from Proto-Slavic (j)azъ →