The sound of gunfire and explosions reached my ears as well as the dying screams of my comrades and my commander shouting orders from the comms. 

I could feel the heavy rattling of my gun even through the mechanical parts of the Worker frame, making the cockpit shake uncomfortably. I saw the enemy forces marching towards us with power far greater than us through the only camera in my frame. 

The bullets of my machine gun fell like rain on them, decimating their military vehicles and completely destroying the few amounts of infantry troops. The same image repeated along the length of our fortress as both Worker Frames, stationary defenses, and the few artillery cannons sent hell to the enemy. 

My comrades were cheering at the view, but this was only the first wave, and also the weakest. The screams of the soldiers and Frame pilots fighting outside and far away from the fortress had died down while we repelled the enemy. Their fate was obvious, death. 

Seconds later, I saw one of the artillery cannons explode as it was hit by a cannon shell. The comms went crazy with orders and shouting as the main forces of the enemy arrived. I pointed my weapon in the direction I was ordered and then I saw them. Infantry Frames aren't like our simple Worker Frames made of cheap materials, unnecessarily bulky and caressing appropriate sensors, they are basically metal cubes without a head and with legs and arms made for mining and building attached to it, Infantry Frames are different. Considerable bigger than us, made with high-quality materials and heads filled with multiple types of sensors, armed with both hand and shoulder weapons. 

Our fire did almost nothing to them, the bullets bounced off their plating. They on the contrary destroyed us with ease, a few shots from a rifle or a single shot from a shoulder cannon was enough to obliterate the Worker Frames. 

"Don't retreat, the TIA can't lose this fortress!" 

Commander Novek voice echoed through the comms, death was inevitable if we didn't retreat now, but it was true that losing this fortress would be a devastating blow. At least we have to hold on until Commander Novek and his pilot squad arrive. 

I pointed my machine gun at the incoming Frames and released a rain of bullets just as the rest of my comrades were doing, but it didn't do much. However, it was useful to divert their attention from the artillery cannons to us. 

Their fire was concentrated on us, a hail of death coming against us. The frame next to me was pierced by multiple rounds at once and fell loudly to the floor, the pilot inside didn't even have the chance to scream. A bullet pierced my frame right shoulder and I quickly hid behind one of the multiple deployable walls scattered around the roof of the fortress. They were sturdy pieces of metal capable of enduring most attacks. 

I heard the bullets hitting the wall but they didn't do much, once they ceased I went out and shot at them again. If I had an advantage over them, it was that I didn't need to reload, our Frames all use Machine guns connected to the storage of the frame, which were modified to store ammunition, they on the other hand use rifles that use magazines. 

While they were distracted with us, the artillery cannons reloaded and shot at the Infantry Frames. The explosion decimated some of the Frames but there were a lot more, and with a shot from some shoulder cannons, another artillery cannon was destroyed, leaving only two left. 

The stationary defenses were long gone and the Infantry Frames were now flying towards the roof of the fortress, how I envy their capability to fly around like that. The concentrated fire of multiple Worker Frames was enough to incapacitate a single Infantry Frame and so we did, but we couldn't keep up. About seven Infantry Frames were taken down, but thirty more reached the roof. 

If the battle wasn't one-sided before it sure was now. The Infantry Frames took quick care of us with their higher maneuverability and firepower, out of the one hundred and twenty Worker Frames fighting, only fifty remained after a few minutes. At that time the Artillery Cannons reloaded again and veered towards some enemies, they shot and destroyed some of them, but they quickly eliminated the cannons. 

A shoulder cannon shot landed beside me and the explosion sent me flying. Luckily I wasn't dead but my Frame was inoperable. The left leg and arm were destroyed, the thrusters didn't respond and the generator was damaged as well. 

I pointed my machine gun at the Infantry Frame that attacked me and pulled the trigger. The bullets bounced off but at the very least, I managed to destroy some of its sensors. 

The enemy Frame pointed its gun towards me, but before it could empty its magazine on me it was tackled by one of my comrades Frame. The Infantry Frame fell to the ground but it unleashed its bullets on the Worker Frame as it did, killing the pilot. 

"To all the TIA forces, retreat now!" 

The commander's orders were voiced through the speakers of the fortress. I expected Commander Novek and his squad to arrive at the scene, but instead, a rain of missiles fell on every Infantry Frame on the roof. The fortress shook because of the explosions and I was almost engulfed in it myself. 

"A Vanguard Frame? Is not commander Novek..." 

Another comrade's voice came from the comms of my frame, he sounded both amazed and confused. Vanguard Frames are the apex of Frame technology, even old generations are powerful enough to annihilate battalions of lesser Frames like Workers or Infantry. 

I could hear the sound of bullets and explosions from inside the cloud of smoke. Eventually, it dissipated and I saw the Vanguard Frame in question. Clad in lustrous black plating, the frame was way much humanoid than the Infantry Frames, but its appearance was demonic. 

Elongated arms with sharp claws at its end were the first thing I noticed, the shoulders were protected by a large plating shaped like a downward half-moon covering the upper part of the shoulders. The head was longer than it was tall, with a large horn pointing forward protruding from the forehead with a long red visor right beneath, from the sides there were a pair of plates shaped like insect mandibles that protected the lower part of the head and part of the visor while leaving a small gap in the middle, making it look reminiscent of an old spartan helmet. The torso was slightly smaller on the lower part with a large bulky protrusion in the chest, there were also a pair of blocks with sensors protruding from the torso right next to the head. The legs were long and mostly smooth with a spike on the knees and feet shaped like a combination of a boot and a heel, there was a long mobile metal plate on each side protecting the upper and outer part of the legs with a similar but bigger plate covering the backside of both legs and a small portion of the torso. There were small linear gaps all along the entirety of the Frame, from which a bright red light could be seen, the exact same color as the visor. 

The Frame held a pair of large revolver-like guns, there was red lighting coming out of the cannon of the guns. On the right shoulder, it had what looked like a mounted laser shotgun, a large weapon that shot scattered laser fire. Meanwhile, on the left shoulder, it had some kind of interchangeable railgun, from its looks it doesn't seem capable of being shot from the shoulder like the shotgun but instead needs to be used with an arm. 

Everyone on the TIA is familiar with Commander Novek and his VF squad and this thing is not one of them, it definitely belongs to a newer generation compared to the TIA Frames. 

"Mercenary Pilot, callsign: Hades. Enemies on the TIA fortress eliminated, proceeding to eliminate the remaining enemy forces" 

The pilot's voice was harsh and almost robotic. Immediately after saying that it activated its boosters and flew away an instant, in just a second, it was no longer in the fortress, and in the place it had been standing it left a burned crater. 

"A mercenary pilot..." 

I exited my damaged Worker Frame and looked around me. The fortress was damaged but saved, filled with dozens of destroyed Infantry Frames. In the distance, I could see and hear loud explosions that shone on a red color. 

"Just who the hell is that?"