He has a wife named Maki, and two sons; the older of which, Masaki, also played professional baseball,[2] and the younger of which is tarento Matt Kuwata.

Kuwata suffered a severe injury to his right elbow while attempting to catch a pop fly in June, 1995, ending his season.

Kuwata considered retirement during the 2001 off-season, but Giants general manager Tatsunori Hara convinced him to remain on the team.

On April 19, 2002, Kuwata pitched brilliantly in defeating Hanshin Tigers ace Kei Igawa by a score of 1–0, and showed he could still be an important part of the Giants' rotation.

[5] In December 2006 Kuwata signed a minor league contract with the Pittsburgh Pirates as a 38-year-old rookie, ending his 21-year stay with the Yomiuri Giants.

Despite interest from the Boston Red Sox and the Los Angeles Dodgers, Kuwata chose Pittsburgh because he thought the Pirates offered him the best opportunity to pitch in the majors.

Kuwata participated in spring training with the Pirates, but injured his right ankle, ending his hopes of making their Opening Day roster.

The Pirates placed him on their Triple-A Indianapolis Indians roster as a disabled player, giving him a chance to work his way up to the majors.

At that time he was 39 years old, which was the oldest debut with the exception of Satchel Paige and Diomedes Olivo in the post-World War II era.

His thesis describes the "Yakyu-Do", the soul and spirit of Japanese baseball, which has been an integral part of the game from its earliest days in Japan during the Meiji Era to the present.