Flowerfell

The first flower appears near their left temple, a small golden bloom that peeks out of their hair when they move around too much. Toriel is the one who notices it, after Frisk had died at her hands and had woken up in their bed by the Ruins.
They sit up quickly, a hand on their stomach where Toriel had hit them with a ball of fire that had broken their soul in half, breathing hard and shaking as they scramble to lift their clothes and inspect the damage.
Nothing.
No burnt clothes, no blood, no wounds. They are in their bed in the house in the Ruins, tangled in sheets and sweating bullets. Flowey appears to be asleep from where he's placed on the desk beside the bed.
When they go into the living room, Toriel is there waiting, like they expected her to be, and when Frisk approaches, she asks if they would like to hear about the book she was reading.
Is it déjà vu when you're sure that you remember – when you have a clear memory of things happening before?
"Ah, did you like the flowers in the hallway, my child?" she asks.
Frisk frowns, and then follows Toriel's line of sight and starts patting their head. There's something soft and thin at the left side and when they try to pull, a stab of pain shoots through their head. Frisk closes their eyes and hisses, staggering as their vision Blackens
"Child?" Toriel has stood up when everything clears, book forgotten on the floor and arms outstretched to catch Frisk should they stumble.
Frisk signs, I'm fine, and gives her a strained smile. It's hard to smile at your mother when you remember them killing you.
Flowey only gives them a confused look when they reenter their room, deciding to postpone asking Toriel how to exit the Ruins again.
"You put a flower in your hair?" he asks.
Frisk shakes their head. Pauses. Looks down at the floor.
They sigh and sit down on the bed. "Don't know," they whisper. "Confused. Don't know what happened. Had a confusing dream," they wave a hand as they rattle off broken words. Their head is still ringing too much to make sense right now.
"I..." Flowey pauses and then clears his throat. "I think you died," he says, "And returned to your last save point."
Frisk raises an eyebrow.
Flowey sighs, "Go to sleep, Frisk."
They lie down, but they don't sleep.

Still, Frisk asks how to exit the Ruins, and still, Toriel stops them, again and again and again, until she decides to destroy the gate to Snowdin herself. And still, she challenges Frisk to a fight, threatening to bake them into a pie, too mad and too raw from having children disobey her before and dying at the hands of others.
Still, Frisk refuses to fight back.
They should be able to dodge now that they've fought the same battle twice, but Frisk jumps to the side too late and the fireball hits their eye. Frisk screams as the heat consumes half of their face and vision, their soul shatters, Toriel murmurs an 'I'm sorry,' and Flowey yells their name somewhere behind them before Frisk feels the ground being pulled underneath their feet –
And when they open their eyes, they're staring at the ceiling of their room in Toriel's house again.
"Frisk?" Flowey whispers, then, "Frisk! Frisk, are you okay?"
Their chest feels too tight when they breathe, and they put a hand on it as they try to steady themselves. Everything is spinning.
"Frisk," Flowey nudges the boot he's planted in and only ends up falling onto the surface of the desk face-first. "Dang it," they groan, letting a vine sprout from the soil they're set in and using it to push himself up.
Tears prickle at the edges of their eyes and Frisk covers their mouth with both their hands to muffle their sobs. Flowey stops what he's doing and looks down instead, leaves curling in.
There's another flower near Frisk's cheek, a few inches from the one on their temple, but he doesn't mention it until morning.

The next time Frisk asks to leave, Toriel looks at the new flower they're sporting with a strange look, but her attention is quickly diverted by Frisk's request. This time Frisk doesn't let Toriel talk them into staying and instead runs down to the basement with Flowey in their arms, Toriel on their heels, shouting in anger.
The only warning they have is Flowey's cry of "Look out!" before heat flares on their back and they stumble and wake up in their bed again.
There's a new flower near their ear.