Born in the city of Ojiya in the Niigata Prefecture, Isa found biathlon after graduating high school and joining the military. Isa debuted in the World Cup in first round of the 2000–01 World Cup in Antholz-Anterselva, Italy. That season Isa made his debut at the World Championships at the World Championships in Pokljuka. He also participated in all World Championships from 2003 to 2009, and then all three World Championships from 2011 to 2013 for Japan. Isa participated in his first Olympics in 2002 and he also participated in the Olympics in 2006, 2010 and 2014. His best individual finish at the Olympics came in the 12.5 km pursuit in 2006, he finished 35th. His best relay finish also came in 2006, a 12th place. His best individual finish at the World Championships came in 2005 in Hochfilzen, where Isa finished 25th in the pursuit. His best relay finish at the World Championships was an 11th which came in 2001 in Pokljuka.