Seiichi is of Japanese origin, meaning 'first' or 'beginning'. It's composed of two characters: 'sei', which means 'birth' or 'life', and 'ichi', meaning 'one'. This name has been traditionally given to firstborn sons in Japan. Seiichi was popular during the early 20th century but has since become less common.
"Between 1919 and 1926, the name Seiichi was chosen for a total of 40 newborns, with the peak years being 1919 and 1920 each seeing 8 births."