You know no one will forgive you, but that's all right. You knew from the start that you don't deserve forgiveness. You were bound to disappoint everyone in the end anyway, so isn't it better for your death to serve some kind of purpose? Freedom for the monsters, and death for the humans. What better purpose could there be?
When you were younger, you used to wonder if buttercups tasted good. Supposedly if you held one under your chin and your chin turned yellow, it meant you loved butter, anyway. You'd never actually tried to eat one, though. Maybe if you'd known they were poisonous, you'd have tried sooner. As it turns out, they taste... what's the best word for it? Godawful. They're not just bad; they're an affront against all that's holy. All told, it's a pretty appropriate way for you to go.
How many have you eaten by now? Twenty? Thirty? Asriel, bless his heart, keeps bringing you armfuls, despite all his reluctant hesitation. You knew he wouldn't let you down. The fact that your SOUL will join with his brings you some comfort, burns as your last candleflame of hope. You're not sure you could go through with this if you didn't have his help. At least, you wouldn't be able to make your death worthwhile all on your own. How could you? It's impossible for someone as ugly and worthless as you to create something pure and beautiful all on your own. You need Asriel.
You do worry, though. It's a comfort to you that you'll be with Asriel forever, but will something bad happen to him after merging with you? He's so good and kind, and however noble the cause, you're still asking him to commit murder. You aren't going to corrupt him somehow, are you?
No, it'll be okay. You'll be dead, and he'll be alive. Naturally his consciousness will win out over yours, if yours even still exists by that point. He'll still be him, and you know he won't let you down. You don't have to worry. Soon it'll be all right.
God, these flowers taste awful. Your guts are already starting to flame and itch and burn. You keep eating them anyway. When your grim determination starts to falter, you look up from your bed at the framed photograph pointed at your bedside.
Asriel, Toriel, Asgore, and you... You all looked so happy. It's so awful, you have to laugh. You can't keep it up, though. Even the barest effort rips and tears at your throat and stains your teeth and palms red. You remember how Asgore looked when he'd been laid out in his own bed, every breath tremulous and wet. Toriel had been so angry, and why wouldn't she be? Your little prank, the one you'd talked Asriel into because you'd thought it would be funny to trick him into making a gross pie and feed it to his dad, nearly killed the most important man in her life.
Maybe he'd survived, but your hope - in family, in a future, in a you worthy of love - had not. Yet again, you ruin everything you touch. They'd been right all along, your bio-parents, your schoolmates, your teachers, everyone from your old village. You were a fool to ever believe you could be anything but a demon.
Your fingers are beginning to blister. Your tongue and throat feel like they're doing the same. The metallic tang of blood bubbles at the back of your throat, anyway, a remainder from your laughing/coughing fit. You wipe your hands on your pants, careful not to stain the sheets; those might be reusable after your death, but your clothes won't be. You don't want to make your adoptive parents have to clean up more than they absolutely have to. Toriel and Asgore will be upset, you think, when they find out what's going on, because they're such good people that they can't stop themselves from caring about an awful thing like you. You'll never understand how you tricked them into it.
They'll get over it eventually. They're monsters, aged in centuries, and you're just a little slip of a human child, barely twelve years old. The time you've existed in their lives can be measured in the blink of starlight. ...Well, no. Not really. But it sounds poetic.
The stars, though. Soon Asriel and everyone will get to see them. It's a nice thought, and you savor it like you savor the bitter blossoms. The lotus is a symbol of enlightenment because it rises above the murk of the world to bloom beautifully. You like to think that the murk that is your entire existence will make the lotus blossom that is Asriel bloom on the surface world for all the monsters. That's how you want it to go, anyway. Maybe it's your considerable selfishness talking, but it would be nice if a rotten empty thing like you could be the stepping stone for a better, kinder world. A world full of monsters. A world without humans.
Death for humans, and freedom for monsters... It's a reassuring mantra, steady like a drum. Death for humans, including you. The world is better off without you in every sense possible, and besides, you need to make up for your sins of existing somehow. This is the best way. The only way. Someday, when he knows everything, Asriel will understand; Asgore and Toriel too. They'll all understand.
But not, you hope, too well.
You eat another buttercup.