Whakaotihia te rerenga e whai ake nei: I whanau a Koga i Kitashigeyasu, Saga, Japan. I tīmata ia ki te mahi judo i te kura tuatahi. I haere ia ki Tokyo i te wa o te kura tuarua ki te whakauru ki Kodogakusha, he kura judo i tae atu ki nga toa koura o te Olympics a Hidehiko Yoshida me Makoto Takimoto. I haere tonu ia i tana maatauranga i te Nippon Sport Science University, a ka mau ia i etahi tohu maha tae atu ki nga toa e rima i te Kodokan Cup me nga toa e ono i te All-Japan Judo Championships (i te wehenga 71 kg katoa). I noho ia ki te tuatoru i te 1987 World Judo Championships i tu ki Essen, ka kowhiria ki te whai waahi ki nga Taakaro Orimipia o te Raumati 1988, i hinga ia i te rauna tuatoru o te whakataetae. I hoki mai a Koga ki ngā Orimipia i te tau 1992 whai muri i tana wikitoria i te
1989 me te 1991 World Judo Championships, engari i whara kino i tona turi maui i te wa o te huihuinga randori (whakatairanga) ki a Hidehiko Yoshida, i aukati i a ia ki te whakamahi i tana tikanga pai; te Ippon Seoinage. I wikitoria e ia te mētara koura i te wikitoria i tenei whara, a i whakawhiwhia ki a ia te Tohu Hakinakina JOC e te Komiti Orimipia o Japan.