Ryūnosuke Ōkoshi, who comes from the northernmost main Japanese island of Hokkaidō , competed in his first FIS races shortly after his 15th birthday . In the first season he managed his maiden win. On March 8, 2005 he made his Far East Cup debut and only one year later he became a winner. In March 2006 he started at the Junior World Championships in Québec and reached 25th place in the giant slalom. In two further JWM participations ( Flachau 2007 and Formigal 2008 ) he recorded an 18th place in the slalom of Salzburg as the best result.
On January 6, 2009 he made his debut in the Zagreb Slalom in the World Cup . After winning the silver medal in giant slalom at the Winter Universiade in China , he established himself in the Far East Cup in the coming winters. With consistently good performances, he qualified for the 2011 World Championships in Garmisch-Partenkirchen , where he finished 28th and 55th in slalom and giant slalom. Two years later he also took part in the World Championships in Schladming and was classified as 36th in the giant slalom. In the 2013/14 season he won the overall ranking of the Far East Cup for the first time with five wins and in March, after two titles in giant slalom (2010, 2012), he also secured the Japanese championship title in slalom for the first time. Nine years after his first World Cup start, he qualified for the second round for the first time on January 14, 2018 in Wengen . In the end, he finished 19th and scored points for the first time.