Gymnastics in Aikido
The gymnastics in an aikido lesson serves to prepare for the following exercises such as the aikido techniques. In Ki Aikido there are no acrobatic movements and there is no extreme stress on the body. Therefore, gymnastics serve less for warming up and more for flexibility and coordination. Mind and body should always be in good condition in everyday life. With Kenko Taiso this should be learned, practiced and maintained.
Kenko Taiso is always done in the same way. A disadvantage could be that it gets boring and the exercises are only carried out mechanically. But there are advantages. The Aikidoka know the exercises after some time and do not have to keep looking at the instructors. So they can better pay attention to the correct execution. They can also do the exercises alone, e.g. practice them at home.
The first video (Shirakawa) is an example how to do the exercises ligth-heartedly. Even if mind and body are unified, the mind can be free.
Doing gymnastics with music can be a welcome change. In Aikido, however, one does not want to depend on it in the long run.
Recommended reading: K. Yoshigasaki, All of Aikido, Part 1, Chapter 1, Kenko Taiso.