The Kana Extended-A block spans U+1B100–U+1B12F, 48 codepoints in Plane 1 (Supplementary Multilingual Plane). 35 are assigned in Unicode 16.0; the other 13 are reserved for future characters.
By script: Hiragana (32), Katakana (3).
By general category: 35 other letters (Lo).
The first 31 arrived in Unicode 10.0 (2017); later additions came in 14.0 (4).
35 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.