Dust coated your hands, your face, your clothes. A mouth stretched upwards in a soulless smile adorned your child-like face and you felt it open as words that were somehow not formulated in your mind rasped into the golden shadows.
'Remember- this is what you taught me.'
Your body moved, and stepped forward stiffly- movements becoming more fluid as your body entered the room. The corridor. A shadowy figure was visible at the end- but?
What the hell?
The smooth shadow stumbled into one of the rays of light melting like butter through the windows- and a strange voice sputtered from it. Your eyes narrowed, the only clue you'd gotten so far as to what your body was thinking. The voice spoke clearly, less nervous than you'd ever heard it before.
'You won't be doing any more killing today.'
The voice's owner was fully exposed in the light, and 'you' shielded your eyes with one hand to see in the brightness. Confident in her movements, the ember-tinged creature took another step forward- and not for the first time, you felt the strings of doubt tugging at your soul, slick with regret.
Suddenly- and painfully- a crack of darkest shadow spread across your soul with a wrenching pull. Pain blossomed in your chest, and you found yourself fighting to stay conscious- in fact, you had an awful hunch that the only thing keeping you from slipping away was this dark consciousness seeping into your body and mind.
Without warning, a rumble echoed throughout the corridor and a missile rocketed towards your body- the thing using your body as some kind of sick host slid sideways and ducked, clucking your tongue as it used your eyes to watch the missile obliterate the door and wall that just seconds ago stood solidly behind you.
'Naughty Alphys,' it chided, and hearing its voice rasp out of your mouth made you want to vomit. 'Play nice. Now, what would King Asgore say if he saw you misbehaving?'
'She's right. What you're doing has to be stopped.'
A deep and intimidating voice boomed through the hall, and you could feel your possessor's complete and utter hatred for this one being- and- was that- fear? You allowed yourself a quail of hope, which was pounded to the ground when you realised what you had done to Alphys. Undyne was her best friend, she had meant the world to her. And Mettaton- you felt terror of yourself, this time, and thinking about the things you had done- you had put it off for so long- filled you with an awful kind of revulsion that made your soul shrink until you felt so, so small.
What about Papyrus? You'd destroyed the only one who still believed in you, your only chance at redemption. Destroyed, crushed like an insect under a boot. And- and with this, you felt bile rising in your throat- what about his brother? Sans must have been... No, you couldn't even begin to imagine how it had affected him. You felt like you were going to throw up.
As you felt your soul begin to ache under the weight of your sins, your possessor began to leap and twirl in a horrifying dance away from the attacks hurled at them, your mouth still stretched into that hateful smile.