Soma's speed on the wing, his excellent man-marking capabilties and his ability to overlap, find space in the corner and center the ball with a high degree of accuracy contributed to a great many goals, both for the national team and for the Kashima Antlers. He was a core member of the team that took part in the 1998 World Cup, claiming 64 NT caps and four goals.
Although Phillippe Troussier's switch to a flat three defence ended Soma's national team career, Soma remained a force to be reckoned with in the J.League for several more years, following his career "peak" at the 1998 World Cup. But in 2000, the year that the Kashima Antlers won their unprecedented treble, Soma was injured in the second-to-last match of the season, and ligament damage kept him out of the lineup for most of 2001. By the time he returned, he had lost his starting spot as well as much of his speed and shaarpness. He would continue on for a few more years, but never regained the form that he showed in his earlier days.
Soma moved to Tokyo Verdy for the 2002 season on a one-year loan to allow him to start regularly. After demonstrating that he was back in decent physical conditions, the Antlers reclaimed him in 2003. But by this time it was clear that he was nearing the end of his career. The Antlers decided to release him at the end of 2003 and he was picked up by Kasawaki Frontale, where he played out the remainder of his professional career.
Since hanging up the boots, Soma has had a successful career in J.League coaching, including a stint at his former club Frontale.