Ostri, also known as the Ostri Republic was a nation on the planet Sera. In antiquity, Ostri was a small but powerful kingdom bordered by the much larger and more aggressive Kingdom of Pelles. In order to prevent their kingdom from being conquered by their neighbor, the Ostrini royal family arranged a marriage between them and the royal family of Pelles, forming the duel Kingdom of Ostri and Pelles. Even after their respective monarchies fell out of power, the two countries were so intertwined that the elected leaders of Pelles would also lead Ostri, as was the case when Yori Deschenko lead both nations during the final years of the Pendulum Wars and the first year of the Locust War.
Before the start of the Pendulum Wars, Ostri and Pelles were some of the first nations to join the new political alliance known as the Union of Independent Republics, becoming leading members of the organization. Eventually the war reached the borders of Ostri, creating a new front and forcing the Ostrinis to heavily fortify their borders, building thousands of bunkers and hundreds of miles of trenches long after the practice of trench warfare had fallen out of favor. This led to heavy casualties for both the Ostrini and the COG attackers.
Despite this, Ostri scientists managed to develop the concept and technology for a space-based orbital energy weapon system, which would eventually be stolen by COG commandos in the last few years of the war, leading to the development of the Hammer of Dawn weapon system which would be used by the COG to wipe out a UIR fleet off the coast of Bonbourg, Ostri, an event which would end the war.