On the surface, this seemingly simple drill has a lot to offer. For clarity, I will describe the drill for the right side only. You can perform the drill from a static or near static position as you learn the mechanics. Once you have the mechanics move on to a moving form of the drill.
We begin with tori taking kote-hineri on uke.
Uke pushes downward to escape the lock.
Tori follows uke’s push, and at the bottom extends uke slightly. Tori would like for uke’s arm to be straight. In the moving form, this slight extension is a balance break.
Tori rotates uke’s wrist and takes kote-gaeshi.
Uke isn’t particularly fond of his new situation, and tries to escape by pulling his hand away. This forces him to bend his elbow.
As uke’s elbow bends, tori floats back to kote-hineri.