The head of the Royal Guard prepared to venture to New Home. Typically, this would be Undyne's return back for the daily report to King Asgore.
But today. Today changed Undyne's life.
Forever.
Undyne finally did it: she killed her first human.
The human was an adorable, little girl who wore a ballerina outfit. She stood, dignified, gracefully moved to avoid spear after spear. In her steadfast Integrity, she refused to ACT in the one-sided battle. She faced Undyne, unwilling to FIGHT or talk back against the excessive taunting. The child even refused to flee from her ruthless attacks. Yes, she stood there, moving in a pirouette and regained her poise, avoiding the flying spears.
Until she didn't, could no more.
While the girl lived and breathed, she carried herself like a princess. She had an unrivaled elegance, a natural spring in her step. She was beautiful in life. So beautiful. So ethereal were her movements, even as her dreamy eyes faded—as her body convulsed under Undyne's spear buried deeply into her chest. She coughed out blood as Undyne stood below her, bringing the human aloft on her pike, skewering the jabbed end further, crimson drops painting Undyne's helmet.
The human let out a pitiful wail that echoed grotesquely around them. A weak whimper lost in the misty cavern's stale air, Undyne yanked out her weapon, fresh blood spilling out from the fatal wound upon her breast.
With a sigh, the girl fell silent.
The temperature seemed to drop amid her death as if it was all not for naught—that she lived on, transcending body and spirit: there is a purpose to this act; there is power in this act, even if it frayed Undyne's SOUL through this sin.
The girl's SOUL left her cold, dripping body, scarlet marring her pink tutu and dainty shoes; the scent of iron filled the mist, the humidity giving the corpse a rank smell. But that SOUL, that beautiful SOUL, that lovely blue light shocked Undyne, who wanted nothing but to lose herself in it. Here lies the real beauty of humanity, Undyne thought with delight she has never known.
In death, she lived. Her determination was—is—timeless. Incorporeal.
It was almost poetic. Almost.
Undyne did not care whether the child was harmless. All humans were the same to her. No, all she cared for were the ends justifying the means. Undyne's sin attributed to breaking the barrier; to free King Asgore's people from millennia of imprisonment. That is all that matters in the end: breaking out of this hell.
Someone watched the slaughter from beginning to end, hiding in the distance and blending in with the cavern's darkness. For Sans the Skeleton, it hurt to watch.
Undyne took the human's blue SOUL floating above the child's bloody corpse and reverently put it in a capsule. She stood still to gaze at the softly glowing heart with admiration, the blue haze highlighting the girl's innocent blood upon her steel pauldrons and chest plate.
Sans turned his back on Undyne, shaking his head.
There is no beauty in death.
With a step forward, Sans vanished.
After Asgore appointed Sans as a 'scout' of sorts, Undyne was not happy in the slightest.
Sans would fall asleep even more frequently while on sentry duty. Worse yet, he had the audacity to set up an illegal hot dog stand. How he could operate four sentry stations within the span of one day baffled her. She paid it little mind. What mattered were results.
Unfortunately, they were abysmal.
Sans produced only mundane written reports, consisting of brief words, such as "nothing here", "nope", "the usual". If Sans felt bored enough, he would end up writing about the most inane tasks. "i made a 'dog." "i made a hotcat today." "i made an apostrophe 'dog today."
Sans was so good at doing the bare minimum that Undyne couldn't fire him, especially with Asgore insisting on keeping him around. "It doesn't hurt to have an extra pair of eyes—or eye sockets," the fluffy pushover would say, to her frustration. It seemed the 'scout' job was only a re-wording of 'sentry'.
And that is what Sans remained in Undyne's eyes—a lowly, lazy, good-for-nothing sentry.
What Undyne didn't know was that Sans's sentry job no longer included making daily reports to her, although he still made them to appease the boisterous fish monster. In actuality, Sans was chosen for the sole purpose of protecting Asgore from human invaders as a last resort. As if that wasn't strange enough, there lay yet another layer on top of another in his duties.
On the king's orders, Sans is to track the movements of humans right after they leave the Ruins. On his command, Sans is to hunt down and execute any human that Sans deemed a threat. Asgore's trust in him was unquestionable—blind, even. It took one fierce battle between the two for Sans to accept the unpleasant task. Being the clear victor, Sans proved to be an astute and dangerous adversary. These attributes were vital to his given role. A role he was ashamed of having, sure, but an important responsibility for him to help bear the king's burden. In plain sight, he was careless, bored, and bordering on eccentric (to the handful that knew his duties) for also having a career similar to Alphys. Sans knew he didn't look like much. But that was okay with him.
Sans knew himself to be akin to a merciless assassin. However, Undyne didn't know this. No, she couldn't possibly know. Not that she wasn't observant, mind you. Sans knew better than that. But when it came to his jobs, it was best to keep her, like everyone else, in the dark. Yes, of course she doesn't know.
And she is never going to be allowed to know either if Sans had anything to say about it.