Gekki Sai Dai Ichi - Attack and Destroy, Introduction Kata No. 1:

The Gekki Sai Kata were formulated by Chojun Miyagi Sensei in 1940 as a form of physical exercise for high school boys and to help popularize Goju-Ryu among the public of Okinawa.

In 1948, after WWII, Miyagi Sensei began to teach the Gekki Sai Kata in depth as a regular part of Goju-Ryu in his own dojo. Until this time, Sanchin was the first Kata taught in Goju Ryu.

Sanchin Kata is physically and mentally a demanding Kata and requires a great deal of time and patience to learn and perform properly.
The Gekki Sai Kata however are easier to learn and perform, and contain dynamic techniques with multiple applications which are more attractive to young people.

These Kata contain the same kanji found in Saifa.

This would suggest that even though these Kata were designed primarily as a form of exercise, Miyagi Sensei included his understanding of combat as part of their makeup.

Most the movements are done with a closed fist and with full power.