This kata is the only one that originated in Isshin-ryu. It was designed by Master Shimabuku in the late 1940s while he was laying the foundation of what was to become our style. However, it seems he did not teach this kata publicly until the 1950s.
One translation of the name is "Son of Old Man" in honor of Tatsuo's grandfather). Another is "Strong Man" which was Tatsuo's nickname due to his reputation for extraordinary power.
In this kata you can see echoes of our other hand kata, notably Wansu and Kusanku, as well as being introduced to squat kicks, sliding spear-hand strikes (nukite) and a spinning elbow strike.