Kaisei has been given to about 137 people in the United States since 1880. It was most common in 2007, which makes it a millennial-parent name.
Its best year was 2007, when 10 babies were given the name, ranking 7881st. The typical living American called Kaisei is about 11 years old today.
Source: US Social Security Administration, national and state name files, 2025 release. Etymology researched and written by our editors. Living-population and median-age figures are our own estimates, described in the methodology.