He is represented by Triple A. Motomiya's elder brother is Ryuji Harada, also an actor.
Motomiya was scouted after his older brother entered the entertainment industry and debuted in 1994 Spur wa Yukue Fumei (Nippon TV).
Contrary to Harada's brother, Harada who often plays a good role, he often plays a villain, a suspicious person, or a role to be killed.
Motomiya's son is a big fan of Heisei Kamen Rider series and his was playing with his son and a rider (a monster), so he volunteered for "my son will be delighted" and appeared in Kamen Rider Blade.
Motomiya's special skills are kendo, MMA fighting, boxing, and baseball.