To get to Azalea (the underground shopping area), go out the JR Kawasaki Station East Exit and take the escalator directly in front of you down to the underground. You'll see the shopping area then.
In the middle of the underground shopping area, there is a large plaza called "Humming Garden" with seating areas.
There are about 100 seats in a variety of seating arrangements, including benches, tables, and sofas.
It's unusual to have such a large rest space so close to a terminal station, especially with table seating!
You can even see people studying or working at the tables. It looks like it would be great for desk work or remote work in Kawasaki, too.
And, since it's easy to access from both JR and Keikyu lines, it's a perfect meeting spot indoors in Kawasaki!
As for how crowded the rest area is, the area around Azalea is often used as a transfer passage between JR Kawasaki Station and Keikyu Kawasaki Station, so it can get quite crowded depending on the time of day.
It can get crowded because it's so easily accessible and convenient, but it's a great place to take a break in Kawasaki.
Why not use it as a meeting spot in Kawasaki or as a place to sit and rest near Kawasaki Station?