Prologue
"Well done. Now then, it's my turn…"
Tanya summoned her Holy Weapon - the SIG MKMS that has slain many.
The light of destruction manifested itself in the realm of the gods, threatening to devour even those who proclaimed themselves as 'gods'.
Such was its power as a weapon capable of slaying even gods. It was proof of its wielder's infinite divine power.
Even looking at the weapon was lethal for the lesser gods, who were immediately burned and their essence absorbed into Tanya's Legion.
The beings calling themselves 'Gods' tremble before the sight of the holy weapon.
"Impossible…What are you?! You're just an ordinary Japanese salaryman!"
Even as the gods attempted to overturn the situation, the divine light of destruction simply washed away their laws - turning them into mere mortals.
"This victory is flawless. Here I come. Take this, you dipshit!"
The holy weapon unleashed a surge of divine energy that washed away the old laws that governed the world and gave birth to a new one.
Not even the collective divinities - or as Tanya called them, 'Being X' could withstand the direct, all-destroying power.
Tanya then turned her attention to a particular divinity, who struggled against the light.
It was a pointless struggle, for anyone shot down was guaranteed a certain defeat. For it was a weapon that could never be dodged, always moves faster than its targets, erases all capabilities of its targets, and subjugates them or completely erases their essence as Tanya desired.
"Uuuuuooooooh, aaaaaarrrghhhh!" the divinity screamed.
Tanya glared at the divinity as if she was looking at a cockroach being stomped upon.
"Wait! Tanya Degurechaff! Let's dis…oooooooooouuuuughhhh! We can't talk about this! Please, don't be too impulsive! What I did was wroooooooo-!"
Tanya Degurechaff revealed a grin.
"It's too late to start bootlicking now.
The divinity was slapped by reality, for he remembered the exchange between himself and the Japanese salaryman that he would reincarnate as Tanya Degurechaff. He had once relayed the exact same words to Tanya Degurechaff. He felt terrified, for the situation was reversed.
The entity reached out his hand.
"Not yet…This is not the end!"
He refused to give up, even as his essence was being eaten by the light of destruction. Even as his own existence was slowly being absorbed into the ever-growing Legion.
He refused to be enslaved and be part of Tanya's Legion of the Undead. For he believed Tanya had no right to enslave and subjugate him in the world of eternal destruction, struggle, and bloodshed.
"You said I enjoyed the act of killing? What if I create a new world based on your statement? Wouldn't it be a blessing to all creation and more importantly, to you, Being X? Although at this stage, you're just a slave of mine. HAHAHAHAHA!"
Tanya Degurechaff let out a cold laughter. Her vengeance, decades in the making, finally bore fruit as she devoured and enslaved Being X.
And thus…Being X's essence disintegrated as he joined the Legion of the Undead. The myriad gods who ruled the worlds were now no more than mere soldiers in Tanya's Legion - seeking to unleash Dies Irae upon all creation.
Mercurius looked at Tanya while exuding an air of irresponsibility, similar to one watching a performance in a theater.
Tanya undid the Formation of her Holy Weapon and watched as the realm of the gods crumbled.
"Anyway, how was Being X?" Mercurius asked. His tone contained a sentiment impossible to be explained by words.
"Not bad," Tanya replied. "Yet, the gods did not fulfill my expectations - for the chains of fate still shackle my hands."
Tanya then paused and looked at her subordinates - the Fangs and Claws of the Demon.
"Although, I have no complaints about having him in the opening performance. With this, my subordinates will know the foes they will face in the future, and understand the land the Day of Wrath will lead to. In short, it was meaningful."
"Splendid. I'm not sure if I deserve those kind words of yours, but I truly appreciate it."
The end of the phenomenon they both fixed their eyes upon was far in the horizon. Yet they will continue to march on.
"My expectations are high." Tanya replied, to which Mercurius affirmed to meet Tanya's expectation as they walked away.
Note: Of course, we all await the true Dies Irae. This is somewhat like a teaser, as the story goes from Tanya's awakening as the Apoptosis of Mercury, to the final showdown between Tanya and the Throne God himself. Being X is just collateral damage, a small fry in the maddened whole of Mercury.