Kawabata is the captain of a high-speed boat that sends the Ushiromiya family to Rokkenjima back and forth.

Spoiler

After the murder incident on Rokkenjima, Kawabata held himself partially responsible for being unable to pick up the family sooner, in spite of the typhoon that otherwise prevented him from doing so. In 1998, he agrees to bring Ange to Rokkenjima in the hopes of finding closure.

(from: Wikipedia)