You'll quickly run into confusion if when you first start Japanese, especially if you try to write Japanese IN English characters (romaji) without studying Hiragana very well at first.
It could be Ji, it could be zi. Or it could be tsu, or tu. Maybe shyu or shu? Romaji is written differently at times. Remember, Hiragana is for sounds only. The hiragana is pronounced one way, Romaji only tries to imitate (not match exactly) the sound in English characters.