The Small Kana Extension block spans U+1B130–U+1B16F, 64 codepoints in Plane 1 (Supplementary Multilingual Plane). 9 are assigned in Unicode 16.0; the other 55 are reserved for future characters.
By script: Katakana (5), Hiragana (4).
By general category: 9 other letters (Lo).
The first 7 arrived in Unicode 12.0 (2019); later additions came in 15.0 (2).
9 characters are East Asian Wide or Fullwidth and take two columns in terminals.
Because it lies outside the BMP, every character here takes four bytes in UTF-8 and a surrogate pair in UTF-16.