The enclosed superfiring B and X turrets of Yubari are identical to the A and Y turrets of training cruiser Katori:
The open A and Y turrets of Yubari are identical to the 5.5 inch turrets on the earlier Japanese 5500 ton light cruisers:
The blast shield protruding over the top of the open A and Y turrets to protect their crews from the blast of the superfiring B and X turrets is somewhat usual in Japanese navy, but is a common feature on British light cruiser and destroyers of the era the featured a large caliber gun super firing over a lower level open turret.
Yubari was Hiraga's pet project to build a test ship to actually validate the new structural and layout design concepts he was formulating in his head. Whether the new ship would turn out to be actually a good investment from combat efficiency point of view was not important. It was suppose to be small and cheap as possible so it would be no great loss if the concepts turned out to be unworkable in practice. In fact Yubari was hopeless as a cruiser, being too small, too weak, and more like a large destroyer than any bona fide cruiser.
But although a dubious cruiser herself, Yubari was a huge success as a testbed. All the things she was designed to test worked so well that they were repeated in all subsequent Japanese cruisers.