Some Japanese syllables which have sliding sounds add a small version of the hiragana for "ya", "yu" or "yo" (ゃ, ゅ and ょ) This is called “yōon”. For example: “sha” sounds like “shi”+”ya” so “densha” (a tram) is written でんしゃ. A small “tsu” っ called a “sokuon” shows a doubled consonant: “Nippon” (Japan) is written にっぽん. Without the small “tsu” the first syllable would sound like the word “knee”. 