[2] Kokubo went on to Aoyama Gakuin University, where he became captain and helped his team win its first 1993 Japan National Collegiate Baseball Championship in his senior year.

[3] Kokubo was selected by the Fukuoka Daiei Hawks in the second round of the 1993 Nippon Professional Baseball draft under the system for expressing a team of choice.

He played with the Yomiuri Giants for three years before signing with his former team (now the Fukuoka SoftBank Hawks) during the 2006 off-season as a free agent.

[6] In 2011, as team captain, he helped lead the Hawks to victory in the Japan Series, winning the Most Valuable Player Award.

[7] On June 24, 2012, Kokubo recorded his 2,000th career hit, becoming the 41st Japanese professional baseball player to reach the milestone.