Early morning, a sliver of sunlight seeped through the gaps in the curtains, casting its glow into the room. Mark opened his eyes as he lay in bed, gazing up at the ceiling.

Mark's eyes held a hint of confusion, perhaps due to just waking up, and his mind still felt somewhat foggy. After a brief moment of adjustment, he reached for his phone on the bedside table to check the time.

Without lingering in bed, Mark got up and dressed for the day. He entered the bathroom, quickly freshened up, and took a few sips from a glass of water on the living room table. Following his usual routine, Mark picked up an unsharpened katana lying nearby, put on his shoes, and headed out the door.

...

Perhaps because it was still early in the day, there weren't many people in the neighborhood. With winter approaching, the morning air had a chill to it.

"Whew."

Mark breathed into his hands to warm them up, just as he did every morning before starting his exercise routine. Mark lived in a neighborhood adjacent to a green riverbank, which was where he went every morning.

He began with a few laps around the river, gradually increasing his speed, and after warming up his body, he no longer felt the cold. Stopping in his tracks, he casually tossed his coat aside, revealing a thin short-sleeved shirt underneath.

Standing at a modest height of 5'7", Mark was not particularly tall, and he had a somewhat lean build. However, the muscles on his arms showed the impressive results of years of training.

"Swish!" He unsheathed the katana from its scabbard. Unconsciously, Mark's gaze became much more intense.

One slash, two slashes, three slashes...

Without much ado, he began his practice. Mark's katana moved like a graceful dragon, dancing in his hand with dazzling speed. Even someone unfamiliar with the art could see that this was a master swordsman at work.

Mark had just turned 30 this year, and while they say that 30 is the age of maturity, he didn't quite see it that way. For him, money and work were never significant priorities. After working sporadically for many years, Mark had begun to feel somewhat worn out. With no pressing material needs, he decided to take a break when he was laid off from his job six months ago.

And this break had led him to where he was today.

...

"Retreat!" Mark muttered to himself softly. Unbeknownst to him, he had been exercising for an hour. With a graceful spin of his hand, he sent the katana into the air without looking, and then turned away.

In that split second, the katana in mid-air fell precisely into the scabbard hanging from Mark's waist.

"Clap, clap, clap!"

"Excellent!"

Applause and cheers came from the onlookers gathered on the bank. Among them were several residents of the neighborhood who had been drawn to Mark's swordplay. Ever since he moved here, this scene had become a daily occurrence.

Mark, unfazed by the attention, nodded slightly to the spectators and donned his coat. He then headed back home.

Upon arriving home, it was just 8 AM. After the workout, he was covered in sweat. Mark took a shower, and then grabbed a piece of bread from the fridge for breakfast.

After breakfast, he checked his bank balance on his phone.

"At XYZ Bank, the current account balance is $4,593."

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"Hmm... still over twenty thousand. I paid the rent not long ago, so it should last for a while." Mark didn't feel too concerned about his finances. Apart from daily expenses and some pocket money, he didn't have many expenses.

This routine continued for two more days. However, on the third day, Mark suddenly found himself falling ill.

Just like any other day, Mark woke up feeling dizzy and weak. He struggled to get up and grabbed a thermometer to check his temperature.

"Beep... 39.6 degrees Celsius."

"Wow, I have a fever!" Mark was a bit surprised; due to his regular exercise routine, he rarely fell ill. It was unexpected to find himself with a fever today.

With no appetite, Mark returned to bed and went back to sleep. This fever turned out to be quite severe, lasting for five days. During this time, Mark remained isolated from the outside world, barely eating, and mostly sleeping.

Little did he know, during those five days of isolation, a global catastrophe was rapidly unfolding.

...

"Knock... Knock... Knock!"

The knocking on the door roused Mark from his sleep. After five days of rest, Mark's high fever had subsided, but he still felt weak.

"Who is it?" Mark wondered silently. Strangers rarely visited him; he had grown accustomed to solitude and quiet in his daily life. Even his close friends rarely came to his home.

"Knock!"

The knocking continued, irregular and persistent. Mark felt too weary to inquire further.

Eventually, Mark got out of bed and slowly made his way out of the room to answer the door.

"Knock... Knock..."

The knocking showed no sign of stopping, devoid of any discernible pattern. Mark couldn't be bothered to ask who it was; his weakened body made him appear tired.

Soon, Mark reached the front door and placed his hand on the doorknob. As he prepared to open the door, a slow, raspy breathing sound reached his ears. Alongside the breathing, there seemed to be a foul odor lingering in the air.

"Weird," Mark thought, and this momentary hesitation caused him to pause in his actions.

"Chomp!" The knocking on the door resumed.

The pungent odor in the air further piqued Mark's curiosity.

Without rushing to open the door, Mark slid aside the door's cover and peered through the peephole to see who was outside.

The person on the other side had their head down, making their face barely visible. They were dressed in filthy clothing, stained with unidentifiable smudges, some red, some yellow...

Through the disheveled hair, Mark could tell that it was a woman.

"A lunatic?" Mark made a quick judgment.

Thinking carefully, Mark couldn't recall recognizing the woman's attire. Deciding that it was best not to engage with a potentially troublesome individual, he opted not to open the door.

He waited in silence for the person to leave.

After two minutes of waiting, the sounds from outside gradually diminished.

"Finally gone," Mark sighed in relief. The incessant knocking had become rather irritating.

Without further thought, Mark intended to slide the peephole cover back into place and return to his room to rest. Inadvertently, his eyes glanced outside through the peephole one more time.

It was this second glance that caused Mark's pupils to instantly dilate, and a chill ran down his spine.