The rounded version of the Higashi 東 stamp is classified as a rare mark. Several of these WP #168 marks have been found in recent years, so they may not be quite as rare as they once were.
It looks like an older float to me, possibly pre-WWII. It measures about 3 inches in diameter.
This float has excellent provenance. It was beachcombed on Kunashir Island in Russia by Olga & Dmitry Sokova.