The club's successes were limited and after the 2008 season, he was offered the chance to go on trial at the Norwegian club Stabæk. His trial was a success, and in February 2009 he was loaned out to the Norwegian champions.[3] He was given the number 10 shirt, which had recently been worn by Veigar Páll Gunnarsson.[4] On 8 March, he made his official debut for Stabæk in the 2009 Super Cup. The league champions won 3–1 against cup champions Vålerenga. Kobayashi played an important part, getting on the score-sheet with a free kick and showing trickery with the ball. Stabæk decided 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 Thessaloniki for 18 months.[5] Kobayashi only appeared in 15 matches for Iraklis. At the end of the 2010–11 season he returned to Japan, signing a deal with Shimizu S-Pulse.
He represented Japan U-20 national team at the World Youth Championship in 2003, where they reached the quarter-finals before being beaten by eventual champions Brazil. He did not start their first group game, a loss against Colombia, but he started the next two which they won to secure a top spot, including a win against England. He further played in the round of 16 win against South Korea, but had to be replaced early in the quarter finals.[11] He also represented Japan U20 at the AFC Youth Championship in 2002, where they came second, after losing 1–0 in against South Korea in the final.