[1] Muguruma turned professional with an amateur record of 2–1 (1 KO),[1][2] and made his debut with a second-round knockout victory on April 9, 1981.
He won the annual Japanese boxing series, All-Japan Rookie King Tournament in the featherweight division in February 1982.
[3][4] In his first defense against Chan Young Park in Moriguchi on May 24 of that year, Muguruma was knocked down from an accidental head butt in the third round.
[1] In September of the same year, Muguruma was tied on points with Wilfredo Vázquez in the fight for the WBA bantamweight title at the Osaka Prefectural Gymnasium.
[5] Muguruma moved back a weight class to fight against Juan José Estrada for the WBA super bantamweight title in Moriguchi in October 1988.