Shima Chikamasu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Chōsokabe clan and the younger half-brother of Chōsokabe Motochika, the sengoku daimyō of Tosa Province.

Chikamasu was born as the fourth son of Chōsokabe Kunichika.  Kunichika had relations with the wife of a retainer having the surname of Shima, who later gave birth to Chikamasu whereupon he received the Shima surname as well.  Excelling in the military arts, Chikamasu joined his older brother of a different mother, Chōsokabe Motochika, in various operations including an attack against the Motoyama clan.

Chikamasu, however, fell ill, and, while sailing toward the Arima hot springs in Harima Province to convalesce, he encountered a strong wind that caused his boat to become stranded in Nasa Bay below Kaifu Castle in Awa Province.  Mistaking the boat as an enemy intruder, Kaifu Tomomitsu (the lord of Kaifu Castle) attacked him.  Despite being weak from illness, he fought valiantly, only to be killed.  Thereafter, Motochika became upset at the loss of his younger brother and attacked Kaifu Castle.

His grandson, Shima Chikanobu, participated on behalf of the Toyotomi during the Siege of Ōsaka but was defeated.  Following a period of incarceration, he became a retainer of the Tosa domain, satisfied with a low-level position by which he could engage in farming with the status of a bushi.  Thereafter, the Shima clan continued to serve the Tosa domain and, after the Meiji Restoration, reverted to the Chōsokabe surname.  The main branch of the family ended so the Shima were compelled to assume the role as the head of the Chōsokabe clan.