Koteda Yasumasa served as a bushō during the Sengoku period.  He was a retainer of the Matsura clan of Hizen Province.

As a member of the Matsura clan, after the death of Matsura Okinobu, Yasumasa backed Matsura Takanobu in the ensuing succession struggle for the headship of the clan.  Later, Yasumasa and his son, Koteda Yasutsune, became Christians.  Yasumasa supported Takanobu as the head of the senior retainers of the Matsura clan until his later years.