ゝ

ゝ U+309D, ゝ HIRAGANA ITERATION MARK ← ゜ [U+309C] Hiragana ゞ → [U+309E]

Japanese Wikipedia has an article on:

踊り字

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English Wikipedia has an article on:

Iteration mark

Wikipedia

• ゞ — voiced

ゝ 

1. (dated) An iteration mark denoting the repetition of the previous hiragana.

   さゝき ― Sasaki

• (Japanese ligatures and scribal abbreviations) 〆(しめ) (shime), 𪜈(とも) (tomo), ゟ (yori), ヿ (koto), 𬼀(して) (shite), 〼(ます) (masu), ヶ (“graphical abbreviation for 箇”), 々 (“iteration mark”), ゝ (“iteration mark for hiragana”), ヽ (“iteration mark for katakana”) 〱 (“iteration mark for multiple kana”),