After the fall of Ichiku no in-jo Castle, Tadakuni supported kaneshige KIMOTSUKI of Osumi Province along with local ruling families of the Southern Court to fight against the Northern Court in Nansatsu region.
市来院城の陥落後、忠国は南朝方の豪族とともに大隅国の肝付兼重を援護、南薩地方で北朝方と戦う。