The time ranked him eleventh in the world that year. He did not manage to defend his national title in Kenya, finishing seventh, although he did gain selection for the 10,000 m final at the 1999 All-Africa Games. There he placed fourth in a race won by world medallist Assefa Mezgebu in what proved to be his final individual race representing Kenya. Returning to the Japanese circuit, he won at the Shizuoka Meet but was second to Julius Gitahi at the Japanese Championships. Maina made his debut over the half marathon distance in 2000, starting with a run of 62:46 minutes at the Tokyo Half Marathon in January, and then a career best of 60:48 minutes to win the Nagoya Half Marathon. He won the 10,000 m track race at the Hyogo Relays in a then world-leading time of 27:18.95 minutes (fifth best that year). He was out of the running in that event at the Kenyan Championships, thus missing a chance to compete at the 2000 Sydney Olympics. He placed fifth at the high calibre Memorial Van Damme at the end of the track season. He dropped out of the top-30 rankings in 2001, and had a low key season with the exception of a win at the Kumamoto Kosa 10-Miler, which he won in a course record of 45:29 minutes. He returned to form over 10,000 m in 2002, taking runner-up spots at the Hyogo Relays and Nacht Van de Atletik meet to rank 14th globally. He also gained team selection for the Chiba Ekiden, running a 5K leg and placing second with Kenya. Maina placed first in the 5000 m among the guest athletes at the 2003 Japanese Championships, with the format now changed so that only Japanese runners were ranked. He was runner-up to Julius Maina (an unrelated Kenyan based in Japan) over the 5000 m at the Yokohama Super Meet and was the winner of the Japanese Corporate title over that distance for Toyota. He placed sixth at the Kenyan 10,000 m trials for the 2003 World Championships in Athletics, so did not make the national team. He came twelfth at the Memorial Van Damme race, although such was the speed of the race his time of 27:22.29 minutes ranked him 14th best in the world that year. After 2003 he had little success in track races. Over the half marathon, he came third at the 2004 and 2005 Sapporo Half Marathon, and was runner-up at the 2005 Nagoya Half Marathon.