I can't believe that I forgot to write an Author's Note! XD So, this is a oneshot, and I don't particularly plan to do anything with it, as I don't know where I'd take it, especially since more than likely it would end up quite similar to the other two Subterranean fanfics on this site.
Regardless, I don't own OPM, and enjoy my 600 words of wonder! :P
Blood was flying everywhere. The sky, red with the fire from explosions. In some places, the piles of corpses reached three or more stories high. The sound of thunder echoed throughout the area. Shockwaves destroyed vast swathes of buildings second by second. Chunks of mangled bodies flew in every direction. The ocean of enemies seemed endless; they were laid out as far as the eye could see. Had he been anyone else, not only would he have already lost all hope, he'd be dead.
Left hook. Right jab. A quick spin to knock them off their feet. A few quick haymakers to make space to let him catch his bearings. Two massive fists out of nowhere to crush him between them. Nope, gone. Giants taller than his apartment block fell before his fists, just like all the rest. He hopped from foe to foe, hardly ever touching the sea of corpses that had become the ground. Each of his punches caused explosions of blood to geyser from their bodies. Dimly, he was aware that he'd been fighting for hours, but he felt no fatigue. How could he? He felt more alive than he had in years. He could almost feel the fire in his eyes, see the heat pumping through his heart, and hear the singing of his muscles as he obliterated more and more of them. The time for talking and witty banter had come and gone hours before; now the only sounds were of the battle itself.
Slowly, but surely, the tide of foes dwindled and died. He stood there, alone, on shambles of highway where it just so happened to be clean of viscera, slowly calming himself in the cleansing rain that had recently started up. He halfheartedly tried to straighten out his blue and white striped pajamas, when he heard rumbling coming from his right.
Erupting from the ground mere yards away from Saitama, an enormous glowing figure emerged. "I see you have taken good care of my children. Come, face the wrath of the Subterranean King!" Four enormous red swords came smashing down upon Saitama, crackling with energy all along the lengths of the blades. The first, he dodged. The second, he deflected. The last two screamed home, burying him under a mountain of rubble. "I see you were not a worthy foe after all, to be downed in the first engagement."
The rubble pile exploded from the force of Saitama's jump, blasting yet another massive crater in that area of Z City. "You'll have to do better than that to defeat me, Subterranean King!" As he said this, Saitama punched in the Subterranean King's chest, to the same effect as all the others of his kind, only much, much larger.
As he fell down from the sky along with the veritable lake of blood and guts from the Subterranean King, Saitama had only one thought before he plunged into the earth. 'I wish there was a way for me to have the battle I so desperately want; this one nearly bored me to tears towards the end.'
Finally entering Z City in earnest, Tatsumaki was speechless once more, until she noticed the squawking in her ear from the radio earpiece she wore. "Tatsumaki, what's going on? Our sensors picked up a massive reading that appeared and then disappeared almost immediately. What happened to the Subterraneans?"
"I don't know who did it, but I can tell you two things. The first, is that every last one of the Subterraneans in Z City is dead." She took a stabilising breath. "The second, is that whoever, or whatever, defended Z City had enough firepower to completely level it." This drew a gasp from the other end of the line. "There are huge gouges going in every direction from the middle." The awe in her voice was palpable; she was clearly struggling to find words. "I'm going to where the fight happened to find whatever did this."