The man'yōgana system was based on a system for writing Sanskrit in Chinese characters called darani (陀羅尼).
In the Nara era, when the man'yōgana were invented, there were no yōon (i kana plus small ya, yu, or yo representing a glide) or sokuon (small tsu representing a doubled consonant) sounds, so these symbols do not have any man'yōgana equivalents. Also, there were more vowels than there are currently, so the man'yōgana below have two vowels where present-day Japanese has only one. This is called the kōotsu (甲乙) distinction.