Russian alphabet - Wikipedia
https://en.wikipedia.org/wiki/Russian_alphabet• і — Identical in pronunciation to ⟨и⟩, was used exclusively immediately before other vowels and the ⟨й⟩ ("Short I") (for example, ⟨патріархъ⟩ [pətrʲɪˈarx], 'patriarch') and in the word ⟨міръ⟩ [mʲir] ('world') and its derivatives, to distinguish it from the word ⟨миръ⟩ [mʲir] ('peace') (the two words are actually etymologically cognate and not arbitrarily homonyms).
Cyrillic alphabets - Wikipedia
https://en.wikipedia.org/wiki/Cyrillic_alphabetsCyrillic alphabets used by Slavic languages can be divided into two categories: • East South Slavic languages and East Slavic languages, such as Bulgarian and Russian, often share the following letters, among others: Й, Щ, Ы, Ь (soft sign), Я• West South Slavic languages, such as all varieties of Serbo-Croatian, often share the following letters, among others: Ј, Љ, Њ, Џ