The term "Imperial Senate" may refer to both the legislative body of the Empire, as well as the structure which houses the meeting place of the Senate. The Senate itself consists of an unspecified number of senators and the emperor himself is present during some meetings, presumably to formally enact legislation voted on by the Senate.
While the emperor theoretically has final authority on matters of state and government, it is actually the Imperial Senate along with the Imperial Army and various powerful nobles who hold the defining political power to influence the Emperor's decisions and even overthrow and replace the current emperor. In this manner, like much of the Empire's society and government, the Imperial Senate is clearly based on the Senate of the real-world Roman Empire.
The Imperial Senate building is one of the largest structures in Sadera, constructed to be an imposing testament to Imperial power, with a large dome visible from most of the city. The building has a roughly circular footprint when view from the air, with square protrusions for the four entrances. The entire structure is constructed of white marble, with numerous ornately carved columns and sculptures on both the interior and exterior. The building is located within a large square or forum, surrounded by a large marble colonnade.
The interior of rotunda of the Imperial Senate building houses the meeting chamber of the Senate. The senators are seated in multiple rows, one above the other, surrounding the central chamber, while the Emperor is seated on a large throne opposite them.
In the Empire, only individuals with super-elite bloodlines and careers were granted the honour of stepping into the Senate Chamber. A highly-placed person would have a chance to steer the ship of state and become a leader of men. Even if one were a low-ranked officer, they would be permitted to brief the senators on the progress of the war, and they might even have a chance to directly address the Emperor himself.
After the swift and overwhelming Japanese victory during the early stages of the Japanese-Empire War, the Senate was divided between those senators that realized that the only chance to survive was to make peace, and a pro-war faction who falsely, or even downright delusionally, still believed they could win the war by some means. After it was discovered that the Empire held Japanese slaves taken in the first hours of the Battle of Ginza, before the Imperials were defeated, the JSDF sent a warning to evacuate the Senate building. Senate building itself was destroyed by an air strike carried out by 2 F-4 Phantom fighter jets armed with laser-guided bombs.
After Zorzal El Caesar used an assassination attempt on Emperor Molt Sol Augustus as an excuse to seize power, the pro-war party gained total control of the senate, while pro-peace senators such as Marquis Casel were branded as traitors.
After the conclusion of the Imperial Civil War, the pro peace faction dominates the Senate while all the pro-war factions being imprisoned or stripped of their privilege.