In March 1582, when Hideyoshi attacked Bicchu Province, Hidekatsu followed him and fought his first battle in the Siege of Kojima Castle of Bicchu Province and also took part in the Battle of Takamatsu Castle of the same province.
天正10年（1582年）3月、秀吉が備中国を攻めるとそれに従って備中児島城攻めで初陣を果たし、備中高松城の戦いにも参加した。