Kaisen is a modern American coinage that pairs Kai, the Hawaiian word for "sea", with the -sen ending of names like Jaxsen and Kasen. Some parents also associate it with the Japanese word kaizen, "improvement", although the name did not arise from it. Kaisen entered the US top 1000 in 2022 and has crept up each year to number 800 in 2025, its highest rank yet.