Zack looked down at the massive black dragon he had slain, its body slumped over the ruins of a collapsed highrise highway, rows of crushed cars and power lines underneath its belly. His app marked the target’s name as [Baal, the Bringer of Calamity], the final boss.

As the last living human, this marked the day that humanity took its final revenge on the monsters that destroyed the world. He had slain the last monster with his own bare hands. The nightmare was finally over. He could hardly believe it, as it had been a hellish four years.

Hah. Four years.

In the first year of the calamity, the world population halved. Half of humanity was wiped out within a year after the portals began to appear. Some were outright killed, while others starved in hiding.

Monsters poured out at an unprecedented rate into major cities, wiping out civilians and governments alike in an endless wave of terror. Human survivors banded together in an attempt to fight back, and fight back they did, until they too were wiped out.

Soon, only one person remained.

A single survivor.

Even as his companions were killed one by one, he managed to survive and grow strong, absorbing each monster he killed into his own body to gain raw physical power. He trained like a madman, meditated every day, cultivated his awakening techniques, and diligently farmed demon crystals to raise his demon summoning app's VIP level to 23.

His name was Zack, and he was the strongest. 

With the black dragon Baal dead, the nightmare had ended, but the flames of humanity were already snuffed out.

“I guess it’s over, huh?” Zack said wistfully.

The dark haired young man stroked a severe scar across his left arm, a memento to a life-or-death battle. Looking down at the ruins of the city he once called home, all that he could see were monster corpses and splattered bloodstains littering what was once a sprawling metropolitan city.

All of that was gone now, replaced by deep jagged claw marks that could be seen everywhere, including on the walls of what was once the city’s largest shopping center. The fifty-percent off promotion for Cosmo Milk was ripped to shreds. Back in the day, that was a heavily endorsed celebrity milk brand.

Yes, he won the fight, but at what cost?

Zack looked down at his cracked mobile phone’s grimey screen as flames billowed all around him. He was standing on top of the rubble of a toppled skyscraper, wind howling to further fan the flames.

Coincidentally, his work office used to be in this very same skyscraper. Not that it mattered now.

The only thing that mattered were the two words that appeared on his phone’s screen.

[Mission Clear.]

[Rewards have been distributed into your inbox.]

The notification was displayed prominently on his smartphone.

Before he could check his inbox, his phone flashed white as more text appeared.

[Warning.]

[Final boss, second phase has commenced.]

“What the hell?” he cursed. “It isn’t over yet?”

He had just won the hellish duel against this monster using every last bit of his strength. He burned every last consumable that he had, and used every trick up his sleeve. But it was not over yet.

The black dragon’s body stirred, its eyes glazed over as it rose to its towering height. As strong as he was, Zack’s stamina was spent. There was no winning this fight now.

The dragon swept down at him with its head, faster than before. The last thing that Zack saw was a flash of its horrendous teeth.

Then darkness.

It was over. The last person in the world had been killed. Humanity lost.

…

The smartphone laying on the ground beneath the black dragon vibrated angrily, as two new notifications appeared.

[An item has been moved from your inbox into your inventory.]

[Regression Coin x1 has been activated.]

…

Zzzzz…

Zack opened his tired, sunken eyes. He tried to sneak in a little nap on his commute back home every day, and today was no exception. The way that the subway car rocked back and forth was kind of soothing to him, and sorely needed after countless mind numbing hours at the office crunching numbers for the client presentation tomorrow morning.

He had grown up rather poor, so he learned to find enjoyment in the small things in life, like a daily snooze on the train and a cold beer after work.

BOOM.

The train swayed a bit all of a sudden as if struck by an earthquake, knocking him off balance. The lights flickered.

[Regression Complete.]

At that exact moment, a flash of light encapsulated Zack’s vision, blinding him. Suddenly, he was hit with an unprecedented headache pain that made his entire body go numb.

“Agh!” he yelled, sinking to his knees and experiencing his head erupted in pain, as if someone had taken a sledgehammer and smashed his skull in. The pain was momentous, and he felt like his entire body was splitting apart in agony. But it wasn’t just physical pain that he felt.

He felt visions flooding into his head, of a burning city, of monsters… the images were fragmented and incomplete, but he felt a deep sense of dread as he realized that these were his own memories of what was to come.

Ba-dum. Ba-dum.

His heart pounded heavily in his chest as he recollected himself. Several people were looking at him with concern, but their focus was more on the preceding tremors.

Zack stood up again.

Despite looking the same on the outside, the dark haired young man carried a different aura to him now. There was a different glint in his eyes now, one of a more mature, war-weary version of himself. The fragments of his memory were not complete, as some of his knowledge had fallen to the wayside during his regression, but he was now cognizant of the fact that he had regressed from a war-torn world back to a time before the dungeon break. And he knew what he had to do.

He could hardly believe that this happened, but this was his new reality.

Zack dug into his pocket for his mobile phone, taking it out to look at the time and date. September 18th, 2087 10:05 PM. His eyes widened in shock.

“Isn’t this the day that that happened?” he muttered to himself in a low voice. He took a look around at his surroundings again. A mother on the phone, cradling her child. A professional looking woman with glasses. That old man in the corner. The highschooler with a backpack slung across his left shoulder.

This was it, Zack thought. Exactly as he recalled it. If he recalled correctly, in exactly five minutes, the train was going to crash.

Zack breathed in deeply, trying to stay calm.

He could barely believe it. Another chance, to do everything all over again…

Emotions flooded into his mind, only to be blunted by the fact that he couldn’t quite remember everything that happened. He retained fragments of the past, and the heartaches that accompanied. Companions slain by monsters. Betrayals. Surviving on dried biscuits and contaminated water for years.

He had to make things go differently this time around. Sentimentality could wait. Only with a clear head could he get his powers back as fast as possible.

Entering into his phone’s home screen, he tried to look for the demon summoning app, only to find that there was nothing there.

“Shit,” he cursed quietly. The world had truly regressed to its previous state, and along with it he lost access to everything that he once had.

The train lurched sideways again, this time far more violently than before. Several people gasped.

“What the hell is wrong with the train today?” the old man with the cane in the corner of the subway car complained angrily.

“It might be that construction project that the city was working on,” a woman answered him.

Zack scoffed. He wished it was just a construction project. He was barely listening, as he was too busy fiddling with his thumbs on his phone at the moment. In a bid of desperation, he opened up his mobile phone’s application store and tried to search for the demon summoning app. Nothing showed up.

Ah, that's right. A memory slowly drifted back into his headspace like an old welcome friend.

He needed to encounter a monster to activate the demon summoning app for the first time. That was his first mission for today.

The train lurched again. This time, the ground was shaking.

“Is it an earthquake?” someone asked.

“If only,” Zack replied.

He knew what was coming next.

This was the day of the first dungeon break, and all of these civilians were about to die.

...

Time to speedrun getting his powers back. Hopefully he didn't get too rusty, he did?