Z before i more closely corresponds to English 'j' or the medial consonant of 'Asia'.
vowel + a
vowel + r
hea 'hair'
"...one-fourth of all the characters used in modern Japanese occur in three-fourths of all the most frequently occurring words. This means that by concentrating on learning approximately 500 select characters, the student is assured of being able to read 75% of all the high-frequency words he will encounter in modern literature." - The Kanji Way to Japanese Language Power.