In the Genko Incident in 1331, he joined the army of the Kamakura bakufu (Japanese feudal government headed by a shogun) to attack Shimoakasaka-jo Castle of Kawachi Province (present-day Chihaya Akasaka-mura Village, Minamikawachi County, Osaka Prefecture) where Masashige KUSUNOKI held up, but later, Chikamitsu joined Takauji ASHIKAGA to attack the Rokuhara Tandai (the office of shogunal deputy in Kyoto placed by the Kamakura bakufu) in Kyoto.
1331年（元弘元年）の元弘の変で、鎌倉幕府方として楠木正成が篭城する河内国の下赤坂城（大阪府南河内郡千早赤阪村）攻めに従軍するが、後に足利尊氏に属して京都の六波羅探題攻めに参加している。