Kaiju Apocalypse by Eric S. Brown, Jason Cordova

He recognized the voice from Zeta squad, and he quickly looked at his tactical display. Zeta was being attacked from both sides by Kaiju, which surprised him. The only way the Kaiju should have been able to flank Zeta was by going through the two other squads, and West was fairly certain he would have noticed Dogs running past.
     
    “Impossible,” he heard someone else from the squad mutter. West found himself nodding in agreement. There simply was no way that they could have managed such a feat.
     
    “They tunneled through the walls!” Smith announced over all comms. “Gamma, get back there and assist Zeta. Alpha, hold position.”
     
    West, along with the rest of Gamma squad, hurried back towards Zeta, whose life signs were rapidly dropping one-by-one. The heavy suits were shaking the tunnel walls with their footfalls, causing a small bit of rubble to fall from the ceiling as well. A larger chunk dropped down onto Gamma Four’s suit, which only West saw. He glanced up and saw a small hole opening up in the top of the tunnel. Yellow eyes appeared from deep within the darkness. He stopped running and tried to jump aside.  He made it, but only just.  The second ambush narrowly missed him, leaving him alive.
     
    Nobody else in Gamma squad survived, however.
     
    A new breed of Kaiju, one spawned from the hellish depths of mankind’s worst nightmares, spilled out from the hole in the ceiling. A horrific cross between spiders and slugs poured forth, their yellow eyes burning in rage as they swarmed over Gamma squad. The men and women struggled to fight them off as best they could, but the new Kaiju left acidic sludge everywhere they touched, dissolving rock, armor and human flesh alike. The brave cries of defiance turned to horrific screams of pain and terror.
     
    West began firing at the new Kaiju, his 105 making short work of the ones he could hit. The others, though, were too close to the rest of his squad, and the slime which dripped from the bodies of the Kaiju was rapidly devouring the new armor which the Minister had previously said was nearly impenetrable.  He tossed two grenades up into the hole in the roof, and shot the Kaiju that was trying to crawl out. Orange slime and blood fell to the floor, landing with a sickening splat!
     
    The grenades exploded above, the muffled concussions shaking the ceiling and causing part of the tunnel to collapse.  He checked his readings but saw nobody else from Gamma still alive.  On the plus side, all of the Kaiju were dead as well.  West turned and ran back to Alpha squad, his breath coming in panicked gasps.
     
    “Cathe! Cathe! Spider-slug Kaiju! They slime everything and it burns through everything!”
     
    “What are you talking about, West?” Smith demanded over the comm.
     
    “Gamma’s gone. Zeta is probably gone, too,” West explained as he slowed his approach to the lead squad. He looked back over his shoulder. “Nothing followed. I don’t think they realized I escaped, but they were fucking slugs with legs, Cathe. Slugs!”
     
    Smith was silent for a minute before she responded. “Beta is being overrun by Dogs. Neither Gamma or Zeta are responding.”
     
    “We gotta be close,” West stated as he rounded the final bend in the tunnel. Alpha squad was waiting there for him, guns pointed in his direction– though not right at him, he noticed. “A new breed of Kaiju? This far down? The Overmind has to be close.”
     
    “We can't stay here,” one of the members of Alpha Squad urged Smith. “Fish or cut bait, Sergeant.”
     
    Smith nodded.  “Wheeler is right. We need to keep moving.”
     
    “Should we move to assist Beta, Sergeant?” Another Alpha member asked.
     
    “Forget that!” West blurted out, interrupting the conversation.  “Our mission is the Overmind.  If we're not already all that's left, we soon will be.”
     
    Smith readied her Mark II suit's cannon, a fresh magazine locking into place.  She had come to a decision.