Kokubo is known to be the mentor to Ayumu Hirano, a Japanese gold medalist in Halfpipe at 2022 Winter Olympics, since 2011.

[5] He was officially assigned as the technical coach to the Japanese snowboarding team for Sochi Winter Olympics, leading Ayumu Hirano and Taku Hiraoka to the Silver and Bronze medals respectively.

Kokubo won his second US OPEN gold at the age of 22 in March 2011, right after his home country Japan was hit by a massive earthquake and following tsunami.

In his winning interview, he confessed how he was saddened by the incident, and really hoped for good for his fellow country men : "I talked to my family and everybody is okay, but I have some friends I still haven't been able to contact."

"[6] Kokubo was criticized for his style of dress on February 9, 2010, after he was seen at the Narita International Airport wearing his Olympic team uniform with his shirt untucked, his trousers hanging low, and his tie loosened.