HIRAGANA · DAKUTEN KANA
zu
づ · paired with ヅ
Sound and use
Modern standard pronunciation generally coincides with ず; づ remains in spellings such as 続く（つづく）.
See ヅ, the katakana counterpart →
Kana represent sounds and spelling functions. They do not have lexical meanings of their own.
How the shape formed
This is つ with a voicing mark (dakuten). Its base form is associated with the source character 川.
History and change
Japanese writers used Chinese characters for their sounds. The source character 川 belonged to that wider practice; the kanji meaning was not inherited by づ.
Hiragana and katakana developed as Japanese syllabaries in the early Heian period (794–1185). This is the script-level period, not a first attested date for づ.
Modern standard pronunciation generally coincides with ず; づ remains in spellings such as 続く（つづく）.
What is documented?
The sources above support the script’s broad period and the conventional parent-character account for づ. A first surviving appearance of this exact modern shape has not been established for this entry.
For a look at earlier hiragana variants, use the NINJAL hentaigana index ↗.