Born in Nara Prefecture, Hiroya started playing baseball in 1st grade for the Yamatotakada Eagles (little league), then for the Kashihara Condor Boys when he was in junior high.

[1] During his sophomore year in Fukuchiyama Seibi High School, his team placed runner-up in the autumn Kyoto Tournament, and won against baseball powerhouse PL Gakuen High School during the Kinki Tournament, where he pitched a complete game (1 earned-run, 10 strikeouts).

In his junior year however, due to the involvement of his teammates in a scandal, their team was banned from participating in games.

[9] With a lean build listed at 176 centimeters, Shimamoto is a southpaw pitcher whose fastballs are clocked at a maximum of 144 km/h.

[10] While he can also deliver sliders and forkballs, he learned the shuuto from pitching coach Yutaka Ohno during the 2014 spring camp.