Kumagai Gumi
Watanabe was born on October 13, 1994, in Yokohama, Kanagawa, in Japan, and grew up in Miki, Kagawa. Watanabe's family has a rich history in basketball. His mother, Kumi, played for the Chanson V-Magic and the Japan women's national team. His father played for the Kumagai Gumi Bruins at the professional level. Watanabe's sister, Yuki, played with the Aisin AW Wings. During his childhood, Watanabe's favorite NBA team was the Los Angeles Lakers and his favorite athlete was Kobe Bryant.