Q. Why there are two ways to write "ji" and "zu" for hiragana and katakana?
A. Both hiragana and katakana have two ways of writing "ji " and "zu." Although their sounds are same in either writing, じ and ず are used most of the time. In a few rare cases they are written ぢ and づ.In a compound word, the second part of the word often changes the sound. If the second part of word begins with "chi （ち）" or "tsu （つ）," and it changes the sound to "ji" or "zu," it is written ぢ or づ.
|ko (small) + tsutsumi (wrapping)||kozutsumi (package)
|ta (hand) + tsuna (rope)||tazuna (reins)
|hana (nose) + chi (blood)||hanaji (bloody nose)
When "ji" follows "chi," or "zu" follows
"tsu" in a word, it is written ぢ or づ.