U+31A1 Bopomofo Letter Zi

The Wikipedia has the following information about this codepoint:

Bopomofo (Chinese: 注音符號; pinyin: zhùyīn fúhào; Wade–Giles: chu⁴yin¹ fu²hao⁴), or Mandarin Phonetic Symbols, also named Zhuyin (Chinese: 注音; pinyin: zhùyīn), is a Chinese transliteration system for Mandarin Chinese and other related languages and dialects. More commonly used in Taiwanese Mandarin, it may also be used to transcribe other varieties of Chinese, particularly other varieties of Mandarin Chinese dialects, as well as Taiwanese Hokkien. Consisting of 37 characters and five tone marks, it transcribes all possible sounds in Mandarin.

Bopomofo was first introduced in China by the Republican government in the 1910s and was used alongside the Wade–Giles system for romanization purposes, which used a modified Latin alphabet. Today, Bopomofo is now more common in Taiwan than on the Chinese mainland, and is after Hanyu Pinyin used as a secondary electronic input method for writing Mandarin Chinese in Taiwan as well as in dictionaries or other non-official documents.