Born in Komuro, Funabashi, Chiba Prefecture, she attended high school in Narita, Chiba and later went on to study at Juntendo University. She began competing in long jump and triple jump as a teenager and by 1994 she had cleared six metres and twelve metres in the events, respectively. She won her first national title at the Japan Championships in Athletics at the age of seventeen, taking the long jump crown. Hanaoka made her international debut later that year and placed eighth at the 1994 Asian Games. She represented Japan at the 1995 Universiade, but it was not until 1997 that she placed among the top athletes nationally, coming second in the triple jump and fourth in the long jump. At the National Sports Festival of Japan, she won her first triple title with a jump of .