Tatsuo at first called what he was teaching Chan Migwa (after Chotoku Kyan's nickname) te/karate (Chan Migwa means small-eyed Kyan in Okinawa hogen; Kyan wore glasses)since Kyan never named his system (according to Joen Nakazato). Maekawa said when he started in 1951, Tatsuo was calling it Shorin-ryu and Sun nu su karate.
In 1951 he called his karate style Sun nu su karate (Sun Nu Su karate was a temporary name until Tatsuo decided to use Isshin-ryu) after the nickname he received from the mayor of Chan. In Tatsuo's family there was a dance called Sun nu su, which means 'son of old man'. Later Shimabuku shortened Sun nu su to Sunsu, also the name of the kata he created: Sunsu kata.
At a special gathering, with his students, on January 15, 1956 he declared that his style of karate should be called “Isshinryu karate”. Isshinryu means “one-heart or one-mind method”.
Eiko Kaneshi, Tatsuo's right hand man asked, "Why Isshinryu, why such a funny name?" and Shimabuku replied, "Because all things begin with one".