Career
In the same year they were relegated from the J-League, which marked his end in Tokyo. He signed for Omiya Ardija at the start of the 2006 season and quickly became their star player. After the 2006 he played his first and only international match.
The club"s successes were limited and after the 2008 season, he was offered the chance to go on trial at Norwegian club Stabæk.
His trial was a success, and in February 2009 he was loaned out to the Norwegian champions. He was given the number 10 shirt, which had recently been worn by Veigar Páll Gunnarsson.
Stabæk decided to not to buy him at the end of the season. On 27 January 2010, Kobayashi signed on a free transfer to the Greek team Iraklis for 18 months.
Kobayashi only appeared in 15 matches for Iraklis.
At the end of the 2010-2011 season he returned to Japan, signing a deal with Shimizu South-Pulse. During January 2013 he went on trial with Vancouver Whitecaps Football Club in the Master of Library Science. He impressed during his trial stint and signed with the club for the 2013 season. The club declined to offer him a contract for the 2014 season and his rights were traded to New England Revolution before the start of the season in exchange for a fourth-round pick in the 2016 Master of Library Science SuperDraft.
In late 2015, Kobayashi received his United States. green card, which qualifies him as a domestic player for Master of Library Science roster purposes.
He represented Japan U20 at the Fédération internationale de football association World Youth Championship in 2003, where they reached the quarter-finals before being beaten by eventual champions Brazil. He also represented Japan U20 at the AFC Youth Championship in 2002, where they came second, after losing 1–0 in against South of Korea in the final.
He made his first cap for Japan in a friendly match against Trinidad and Tobago on 9 August 2006, coming on as a 56th-minute substitute for Koji Yamase.