The white piece of plastic floating in the reservoir is to keep the fluid from sloshing inside the reservoir so badly that the master cylinder could such in an air bubble. That sure isn't likely to happen unless the bike is upside down (at which point sucking in a small amount of air into the clutch or brake system is the least of your concerns) but the plastic reduces the odds even more.
You can use any brand / type of DOT 4 brake fluid you want or have access too. But this is the first time I have seen the 'oil / tire thread' type of debate used for brake fluid.
Kawasaki does not make brake fluid so it is very unlikely that they have the best / magic formula for the brake fluid used in their bikes. Besides, even if that were the case, perhaps Honda brand brake fluid has even more of the special motorcycle agent in their re- branded brake fluid.
Brian
This week I changed the brake and clutch fluid on my '09C14 for the first time. After I removed the front brake and clutch master cylinder metal covers and plastic/rubber gaskets, there was another piece of what looked like styrofoam floating in the brake fluid. What is the purpose of this piece? Maybe to help prevent splashing of the fluid inside the reservoir? I have not seen anything like this on any other bike before.
Also, is it better to use Kawasaki brand DOT 4 brake fluid? Someone told me it has some additives that are better for motorcycle use. Is this true? I typically use Carquest brand DOT 4 brake fluid.
