In April 1995, Oku was selected Japan U-20 national team for 1995 World Youth Championship.

After 1998 World Cup, in October 1998, Oku was selected Japan national team by new manager Philippe Troussier.

In 2013, Oku was arrested by Kanagawa Prefecture police after he threatened to kill Hinako on multiple occasions.

[6] On the morning of 17 October 2014, Oku was killed following a car accident on Miyako Island.

[7] He was driving on a prefectural road at about 4:25 a.m. when his car veered into the opposite lane and struck a telephone pole.

[8] According to police, he was transported to a hospital, where he was soon pronounced dead from a broken pelvis and other injuries.