While the older brother went on to create his own new style of karate, Eizo quickly moved up the ranks in Shōrin-ryū (Shōbayashi).
By the time Shimabuku was a teenager, he had attained the physical level of a person six years his senior.
Motobu had had many teachers for short periods of time, including some notable ones such as Anko Itosu (Shuri-te), Sokon Matsumura, and Kosaku Matsumora (Tomari-te).
As a young man in Kyan (Chan) (チャン) Village, he discovered a way to bind tiles to the roofs of homes without using mud, which had been the traditional way.
During World War II, as part of the boeitai, he was forced to help construct the airfield in Kadena with his horses and carts.
Shimabuku continued to study and develop his skills in both Shorin-Ryu and Goju-Ryu but he was not satisfied that either style held the completeness he was looking for.
During the late 1950s and early 1960s, he continued his study of Kobudō with one of Moden Yabiku's top students, Shinken Taira.
During the late 1940s Shimabuku began experimenting with different techniques and kata from the Shorin-Ryu and Goju-Ryu systems as well as Kobudo.
He renamed his Chan migwa-te style "Sun nu Su-te" in about 1947 after having trained with Chojun Miyagi "Isshin-ryū" on January 15, 1956.
[3][4] By the early 1950s Shimabuku was refining his karate teaching, combining what he felt was the best of the Shorin-Ryu and Goju-Ryu styles, the weapons forms he had studied, and his own techniques.
Upon announcing his decision to start a new style, many of his Okinawan students left, including his brother Eizo.
[5] The emblem of Isshinryu no Megami was drawn from Shimabuku's description by Shosu Nakamine, Eiko Kaneshi's uncle, and was chosen to be the symbol for Isshin-ryū karate.
The first of the Marines to bring Isshin-ryū karate to the United States were Don Nagle and Harold Long.
Harold Long returned home to Knoxville, Tennessee, and opened his first dojo at the Marine Reserve Training Center.
Returning later were Harold Mitchum, Sherman Harill, Steve Armstrong, Ed Johnson, Walter Van Gilson, Clarence Ewing, George Breed, Jim Advincula, Bill Gardo, and Harry Smith and others.
George Breed began teaching Isshin-ryū Karate in Atlanta, Georgia, in 1961, and then, in Gainesville, Florida, from 1966 to 1969.
The first, was to Pittsburgh, Pennsylvania, in 1964 from September to late November, sponsored by James Morabeto and William Duessel.
While visiting the dojo of Steve Armstrong (1966), Shimabuku was filmed performing all 14 Isshin-ryu kata as well as some basic exercise and self-defense techniques.