In addition to the
basic hiragana sounds, other sounds can be made by
combining two
characters.
The two
groups of characters that can be combined are the characters ending in 'i' and the characters beginning with 'y'.
An 'i' character is written normally, with a small 'y' character next to it.
It seems that the
resultant sound contains a 'y' only if a character already exists that is the same as the
combination without the 'y'.
For
example, "sha" is written by combining the "shi" and "ya" characters. (しゃ)
"Cho" is written by combining the "chi" and "yo" characters. (ちょ)
"Ryu" is written by combining the "ri" and "yu" characters. (りゅ)