This was not what he was expecting his day to contain when he woke up that morning. No, he was expecting it to be like all the other mornings where he awoke at home alone, made himself tea and breakfast before going to his garden to care for the blooms there. It was a routine that he'd grown used to over the years and it was almost comfortable save the loneliness that plagued it. What he wouldn't give for the companionship that he'd once had before his wife left. He knew and understood the reason why, the disgust she'd had with his plan to take the human souls. However, he just… He just wanted what was best for his people and felt this was the best way.
Mentally the ruler of monsterkind shook away the morose thoughts and emotions dealing with the absence of his darling wife to focus instead on recalling the moment that brought him to this point. The phone call with his Royal Scientist Alphys as she wailed in a panic about something in the CORE going desperately wrong. It had to do with what was powering the great machine… or was it the by-product of the process? He couldn't recall and quite frankly this wasn't the time for reminiscing. He quietly scolded himself for such a waste of time as he came back to the present, staring at the door once more.
There were two things of note happening in the CORE at that moment as far as Asgore could see. One was the siren blaring impossibly loud, ringing in his ears constantly that made him want to cover them and run like all the other monsters that worked here. The second and more pressing matter was the great vault door he stood in front of was bulging, straining to contain whatever breach was happening on the other side. Even with the siren's blaring noise the king could still hear the metal groaning and bolts ricocheting as they gave way to the strain from his safe distance away. All this caused his fur to stand on end at the immeasurable wrongness he could feel from beyond that door.
This time as he looks to the door he noticed something strange was leaking from the cracks and crevices forming due to the bulging faults forming. It was black, the blackest substance he's ever seen but more concerning was how it writhed and shifted as more of it leaked through the door as if it was trying to pull itself out further. It sent shivers down his spine and he clutched his trident tighter to himself as he steeled himself. He couldn't panic and flee like the others. Asgore knew this but it still didn't make it easier to stand there before this unknown threat. He was the king and he would protect his people.
The monarch took a deep breath before turning to look into the camera nearby and nodded his head to it. He knew Alphys was watching, knew that she could open this barrier from the safety of the Lab. Hopefully all the workers had fled from the CORE by now and if not that they were far enough away that this wouldn't affect them. He watched as the light above the door came to life, flashing and adding another blaring horn to the cacophony of noise to signify the door opening and Asgore braced himself. Whatever this substance was he would do his best to investigate what it was and would try to get rid of it.
The second that the door cracked open it was like the floodgates were unleashed and the black ooze spilled forth. It was bubbling, roiling, and pulsing forward making a beeline toward where he stood. Asgore was frozen for a moment, staring in disbelief that this substance seemed to have a consciousness or awareness of its surroundings. Or perhaps he was overthinking this in his anxiousness over the situation. However that second of being frozen ended as he finally moved forward, eyes brightening as he summoned his magic to swing his trident in a brilliant blue arc to try and force it back while it moved forward towards him.
The gelatinous ooze recoiled from the hit, bubbles bursting to release a hissing sound. It seemed to Asgore that the substance actually felt pain from that and it emboldened him. If he could just back it away, force it back into containment his people would be safe. He summoned forth fire from his hands as he directed the blaze to the threat. It recoiled further, backing away from the heat and light coming from that attack. Asgore continued his assault, attack after attack, giving whatever this thing was no room for recovery and making it yield to his might. It continued to retreat, nearly all back behind the door once more and Asgore never relented. He would protect his people. He would.
It was all working in the King's mind as he pushed the substance back. It would soon be over and he could rest knowing that his people were safe but then things changed in a second. Suddenly it lashed forward with its own attack. A whip formed from its substance raced forward and wrapped around the king's arm as he prepared another fire attack. Asgore let out a cry of alarm and pain at the glacial coldness of the goo wrapped around his arm as he worked to pull it free. He managed to do just that and with his arm free he watched in horror as it began to darken at an alarming rate where the goo was. And then it began to spread up his arm and he faltered. It hurts! It was freezing where it touched, a painful cold that made even his fire feel lukewarm.
That moment of weakness was all this thing needed as it began its own assault. Globs of it were flung towards the king which he managed to deflect with his trusty trident. That is until it began to stick to the weapon, changing and corrupting it, turning it into that same substance. This all made Asgore stumble back, trying to dodge away in a haze of cold and pain from the mass that reached for him. It was no use though he couldn't avoid it all as it latched onto his injured arm and legs, spreading upward from there. It was unimaginable the amount of pain this caused, how it bogged down his mind so that he didn't even realize he was screaming out that agony. A single thought flitted through that haze of pain and cold - protect his people… protect his kingdom… protect… protect me… prOtecT ME!
Fear driving his actions at this thought that clearly was no longer his own he used all his might to pull free of the mass, ignoring the agony and cold that covered half his body and he tried to flee. Tried to run from this mass of consciousness and darkness. Tried to ignore the thoughts still lingering in his mind that were not his own, that were bogging down his movements and willpower. Tried to ignore the spreading pain and cold he looked to the camera closest to him and with what little power he did have left shouted.
"Alphys…! Alphys sound the alarm of this threat! Of this Void! Make sure all monsters know of us, keep them away from us! … keep them… from… becoming one with… us."
The longer he tried to fight it, trying desperately to maintain control of his mind to give this command to his scientist, the less he found the willpower to move. He didn't even notice as the Void surrounded him and began to cover him, corrupting more and more of him. How his thoughts no longer belonged to him alone. He was of them now and he couldn't understand why he'd fought so hard to escape. He would protect himself, themselves, from any threat. They needed to escape, to gain more power to free themselves from the prison that held them for so long.