Seiji is a distinctive boys' name in United States, ranking #5587 in 1997 with 11 recorded births. The name reached its all-time peak in 2007 with 19 births ranking #4951. Since 1996, the popularity has increased by 37.5%. In 1997, approximately 1 in every 171,372 boys born was named Seiji. FALLING Recent data shows the name is currently falling.