Kazunari Okayama (岡山 一成, Okayama Kazunari, born April 24, 1978) or Kang Il-Sung (Korean: 강일성; Hanja: 康一成) is a former Japanese football player of Korean descent.
In 2002, he moved to J2 club Kawasaki Frontale and became a regular player as right defender of three backs defense.
He played many matches as mainly center back and the club was promoted to J1 end of 2005 season.
After a half year blank, he moved to South Korean club Pohang Steelers in July 2009.
This biographical article related to a Japanese association football defender born in the 1970s is a stub.