16 characters in the Katakana Phonetic Extensions Unicode block.
U+31F0KATAKANA LETTER SMALL KUU+31F1KATAKANA LETTER SMALL SIU+31F2KATAKANA LETTER SMALL SUU+31F3KATAKANA LETTER SMALL TOU+31F4KATAKANA LETTER SMALL NUU+31F5KATAKANA LETTER SMALL HAU+31F6KATAKANA LETTER SMALL HIU+31F7KATAKANA LETTER SMALL HUU+31F8KATAKANA LETTER SMALL HEU+31F9KATAKANA LETTER SMALL HOU+31FAKATAKANA LETTER SMALL MUU+31FBKATAKANA LETTER SMALL RAU+31FCKATAKANA LETTER SMALL RIU+31FDKATAKANA LETTER SMALL RUU+31FEKATAKANA LETTER SMALL REU+31FFKATAKANA LETTER SMALL RO