Stars Without Number
Yamamoto was settled in cooperation between a few Japanese corporations and the Terran Mandate. After a few decades, the settlers grew tired of governance from the increasingly bureaucratic and ineffectual Mandate. Allied with a few other systems, they fought a long war with the Mandate, and their ally, the Sforza Corporation. Before the war could be settled, the galaxy was hit by the Scream.
Yamamoto fared well during the scream, compared to most of the surrounding systems. Within a century, they had enough military power to take control of the far more populous Kawara, in a nearby system, and have since taken control of other planets and sectors.
Yamamoto is primarily a water planet, with the population living on a series of archipelagos.