Hentaigana

Hentaigana (変体仮名?, "variant kana") are historical variants of modern standard hiragana. They are a legacy of man'yōgana, where many different kanji could be used to represent the same sound value. As the man'yōgana became simplified into cursive forms, multiple hiragana, including the hentaigana, was the result. Many derive from differing man'yōgana characters, but some are the result of differing styles of cursive writing.