Nishi won the Mughal gold medal at the 2003 Junior World Championship. He made his World Cup debut on December 6, 2003 in Ruka , where he finished eleventh in the Mughal competition. In his first season this was by far his best result, in the following winter he did not get past 18th place. In winter 2005/06 he only played the last two World Cup competitions of the season. On February 2, 2007, he was second in the Moguls competition in Voss ; it remained his only podium in the World Cup to this day.
In the 2007/08 World Cup season, Nishi was classified in the top ten twice, and once in the 2008/09 World Cup season. At the 2009 World Cup in Inawashiro , he surprisingly won the silver medal in the dual moguls competition, where he had to admit defeat to the Canadian Alexandre Bilodeau in the finals. With two more top 10 results in the World Cup, Nishi qualified for the 2010 Winter Olympics , where he finished ninth in the Moguls competition.
So far, Nishi has been among the top ten in the 2010/11 World Cup season. At the 2011 World Championships in Deer Valley , he surprised again by winning the Dual Moguls bronze medal.