Nishishita competed in his first international jumping at the Junior World Championships in 1998 in St. Moritz , where he won the silver medal with the team on the K85 hill. On February 5, 1998, he then made his debut in the ski jumping World Cup . When jumping from the large hill in Sapporo , he was able to win his first World Cup points with 20th place. At the Junior World Championship in 1999 in Saalfelden am Steinernen Meer , he won the gold medal in individual jumping on the K85 hill. The 1999/2000 World Cup season was the most successful season of his career. With seventh place in Sapporo, he was able to achieve his highest individual placement in the World Cup and also jumped into the points in almost all competitions. He then finished the season in 32nd place in the overall World Cup standings. From 2002 Nishishita started exclusively in the Ski Jumping Continental Cup , in which he had already participated. However, he could not achieve any successes in this series until 2005. Since 2005, Nishishita has only jumped at the national level. On March 22, 2008 he retired from active sport together with Yūsuke Kaneko and Sōta Okamura after participating in the 9th Itō-hai Season Final Ōkurayama Nighter Jump Taikai .