You don't understand. You just don't understand.
You don't understand how they all could be so nice to you, so kind, so gentle.
After all, you've never done anything right in your life. They really have no reason to love you, no reason to appreciate the things you do, no reason to care about your well-being.
All you've known all your life is how to accept that anything and everything that happened was all your fault. It wouldn't even matter what it was. Heck, someone on the other side of the planet could fall deathly ill and they'll find someway to blame you for it.
All you've known all your life is how to stay quiet and out of the way to the best of your ability. You're always hiding in your room the moment you come back home, listening in fear to the sound of your mother and father violently arguing. You would cry yourself to sleep every night hiding under your bed covers, jumping to the sound of each crash and bang out in the living room, hoping and praying you didn't do anything wrong earlier for them to have an excuse to fling their wrath upon you.
All you've known all your life is how to be the absolute perfect child. You were never truly good at it, and the mental scars of past beatings really showed. The scariest things in the world were no match for the horror that were your angry parents. You always ended up trying too hard to please them, and often you would slip up one way or another and be repeatedly punished for it.
Your mother and father were unsurprisingly the neglectful, overly strict, and abusive types. It was no surprise you were just an accident when your parents were unprepared and unprotected, and they absolutely despised needing to own up to said accident by caring for you. They would fight every night over who needed to take care of you the next day, and more times than not they'd finally agree to just let you fend for yourself once you got back home from school.
They would neglect you and refuse to give you the proper love and attention a young child needs to grow. They wouldn't feed you most nights, so you had to rely on lunch you got at school - that is if your bullies didn't trip you to make you spill it or just simply throw it off the table and onto the ground - to keep yourself fed. You would always eat very little during lunch so your could bring just enough back home to barely make it through the night. Your parents didn't always refuse to feed you, though you often wish they did; what they would give you would be disgusting slop made from the remains of whatever they had that night mixed with boiling-hot water and occasionally served with a slice of stale or moldy white bread. Sometimes you'd get sick from it, and - surprise, surprise - your parents would get angry at you for "not appreciating their attempts to care for you".
Your parents were also extremely strict, and they believed in violence being the only punishment, though on occasion they'd also do other things on top of beatings like ban you from hanging out with the one friend you have after school for a month. A lot of the time these punishments end with you unable to sit right for weeks on end. You have been trained not to step out of line, yet sometimes you just couldn't put your teachings into good use at the right moment, and you know you'd instantly regret it for the next few weeks.
You were taught and trained that you were useless, that you were a waste of time and space, that you couldn't do a single thing right. So... Why didn't they think so? Why do they act the way they do around you with such compassion and love?
Why does Toriel make you butterscotch-cinnamon pie and let you sleep in her lap as she lovingly strokes her filed claws through your hair?
Why does Papyrus enjoy making puzzles and spaghetti for you to test?
Why does Undyne hug you with just enough strength that lets you know she'll never let anyone hurt you ever again?
Why does Alphys like to nerd out with you and have friendly debates on the quality of animes and science?
Why does Sans always strive to make you smile and laugh with his puns and jokes?
Why does Asgore talk so gently and kindly to you, as if speaking too abruptly could shatter you like glass?
Your parents told you you didn't deserve any of the things the monsters give you now. You don't deserve anyone's compassion, anyone's attention, anyone's hugs, anyone's company, anyone's humor, anyone's gentleness.
So why do the monsters choose to give these things to you regardless?
You don't understand.
A/N: So yeah, I don't normally write stuff like this, at least as far as child abuse goes. I'm sorry, I'm just a very sadistic person sometimes. But this kind of stuff only stretches out to fictional characters, not people in real life!
Also, this was heavily inspired by bkwrmnlvnit's The Plans of Monsters and Men, which also has child abuse among other trigger warnings. But it's still a VERY good story! The writing is absolutely outstanding, and it really makes you sit on the edge of your seat, anticipating what's next to come.