Onaga Mitsudomoe is a kind of Japanese family crest "Tomoe-mon". It is a drawing of a tail that is elongated and a smaller head than the normal "three-way" (the round part in the center is "head" versus the thin part on the outside is "tail"). It is used by the Settsu Arima clan and others, and the Arima clan is especially called "Arima Tomoe".
Own work
Mukai