72 characters — gojuon base, voiced (dakuten), semi-voiced (handakuten), and the modern ヴ extension
ー
chōonpu (長音符)
Extends the vowel directly before it. コーヒー → koohii, not "ko-dash-hi-dash." Not a sound of its own.
ッ
sokuon (促音)
Doubles the consonant that follows. マッチ → macchi, ベッド → beddo. Small — easy to mistake for big ツ (tsu).
ャ ュ ョ
youon (拗音)
Small ya/yu/yo — fuses with the preceding consonant into one syllable: キャ (kya), シュ (shu), ジョ (jo).
ァ ィ ゥ ェ ォ
extended vowels
Small vowels used to build foreign sounds not in the base syllabary: ファ (fa), ティ (ti), ウィ (wi), チェ (che).