The surname "Sei" (清) is of Japanese origin and can be found in various regions of Japan. It is often associated with meanings related to purity or clarity, as the kanji character 清 translates to "clear" or "pure." Surnames in Japan typically reflect geographical features, occupations, or characteristics of the family. In Japan, surnames like Sei may also be linked to historical figures or local clans. The name can be found in various forms, including variations in kanji, and is sometimes used as a given name as well. Understanding the context of the surname can provide insights into family heritage and regional history.