As the Japanese language has evolved over time, some syllables have merged. language-reforms have dropped from common use the corresponding letters of the Japanese syllabaries, hiragana (ひらがな) and katakana (カタカナ). These letters are sometimes used in ainu and okinawan.
Particularly, obsolete kana include ゐ/ヰ [i] and ゑ/ヱ [e], usually transliterated ⟨wi⟩ and ⟨we⟩.
This tag applies to any question asking about those obsolete kana.