Hachimura was born in Toyama Prefecture in Japan to a Japanese mother, and Beninese father, Zakari Jabil. His given name, , means "base" or "fortress" in Japanese; the name was given to him by his grandfather because he was a big fan of baseball (the character 塁 is also used for "base" in context of baseball). His surname is from his mother's family register. He has three younger siblings – one brother and two sisters. Hachimura's younger brother, , played basketball at Tokai University in Japan. In his childhood, he played baseball as a catcher and pitcher. On December 29, 2013, Hachimura led the Meisei High School basketball team to its second title in the All-Japan High School Tournament, scoring 32 points in a 92–78 win over . In 2014, he helped his team win the tournament for a second straight year. In April 2015, Hachimura was invited to the Jordan Brand Classic, where he recorded nine points and five rebounds in the International Game.
