Kanazukai (仮名遣?, "kana usage/use") are the orthographic rules for spelling Japanese in kana. All phonographic systems (of which kana is an example) attempt to account accurately the pronunciation in their spellings. However, pronunciation and accents change over time and phonemic distinctions are often lost. Various systems of kanazukai were introduced to deal with the disparity between the written and spoken versions of Japanese.
The former mainstream kana usage, or the Kyū-Kanazukai (旧仮名遣, "old kanazukai"), is based on classical texts, especially man'yōgana. Created by Keichū in the early Edo period, it is also known as the Keichū Kanazukai. It was the mainstream kanazukai until the Gendai Kanazukai was introduced in 1946.
There were other minor systems throughout history that are now defunct:
Kenny you almost made it,
I'd say you were halfway there
Kenny your hands are frozen,
and this is so unfair
What would you do,
given a chance to meet God?
Where did you go, why did you die,
I was a doctor, so where was I?
Kenny the moment's passed us by,
moments turn to days
Turning confidence away,
self assuredness to shame
What would you do,
given a chance to meet God?
Where did you go, why did you die,
I was a doctor, so where was...