Undetermined

Frisk leaves Napstablook's house, his left arm in a makeshift sling. He sighs and ventures further into Waterfall, "This place is bigger than I remember.."

He keeps walking, passing a cave until he gets to a plaque on the wall. He stops and reads the words inscribed on the glowing stone, "Hurt, beaten and fearful for our lives, we surrendered to the humans. Seven of their greatest magicians sealed us underground with a magic spell. Anything can enter through the seal, but only beings with a powerful soul can leave."

He turns away and keeps walking. He sees another plaque on the wall just as he gets to a path leading past two waterfalls. Echo flowers adorn the path, sending soft indescribable whispers through the cavern. He shivers and reads that plaque as well, "There is only one way to revere this spell. If a huge powers, equivalent to seven human souls, attacks the barrier it will be destroyed."

He steps into the water and wades to the other side. Another plaque adorns the wall and he frowns, "I remember this story. They need human souls to even get past the barrier. Duh, that's why they're trying to kill me."

He shakes his head and keeps walking. He wades through another body of water and he enters a new room. A room completely pitch black save for the path lit by magic mushrooms. He follows the path until he enters a new room. Like the last, this room is pitch black except for the light of lanterns. The lanterns start to fade and as he follows the path, he touches them to make them light back up so he can see where he's going.

He sighs, "I could go back and visit the Tem Village, but.. I don't really need to interact with them.. I'll just.. Keep going.."

He leaves the lantern room and finds himself in a dark cave with water covering the floor and a long echo flower across the way. He smirks dryly, heading towards the echo flower, "Look behind you, Frisk."

He gets to the flower and taps it. He hears his voice ring out in echoes, "Look behind you, Frisk."

He turns around as he hears heavy footsteps thud through the water and he sees Undyne, still clad in armor, coming his way. He looks at the ground as she approaches. She stops moving and he hears the anger in her voice as she speaks, "Seven. Seven human souls is what we need to break the barrier. Six. That's how many we have. So stop running and just give me your soul. Your continued existence is a crime, human."

Frisk shakes his head, "Trust me.. If I had one, I'd give it right over.."

Undyne growls, "Is that a joke? I'm not laughing!"

Her spear appears and she roars, running at him with it. Out of nowhere, Monster Kid gets between Frisk and Undyne, "Wait, Undyne! I'll help you fight!"

"Heh.." Frisk wipes tears from his eyes as Monster Kid frowns, "Wait.. Who's she fighting?"

Undyne grabs and grabs Monster Kid by one of the horns on his head. He yelps, "H-hey! You won't tell my parents about this, right?!"

A new pathway lights up and Frisk follows it to a corridor filled with water and echo flowers. Some kind of magic golden lights shine and float about the dark corridor. The sound of rushing water seems to calm Frisk, if only a little. As he walks through the water, the echo flowers repeat a passing conversation:

"Hmm.. So, if I say my wish.. You promise you won't laugh at me?"

"Of course I won't laugh!"

"Someday, I'd like to climb this mountain we're all buried under. Standing under the sky, looking at the world all around.. That's my wish."

Frisk hears laughter and then the first voice speaks again, "Hey, you said you wouldn't laugh!"

The second voice sighs, "Sorry, it's just funny. That's my wish, too."

At the end of the corridor is another plaque and a passage leading to the right. Frisk touches the plaque, whispering the words written there, "However, there is a prophecy... The 'angel'. the one who has seen the surface.. They will return, and the Underground will go empty."

Tears fall down Frisk's face, "I made the Underground go empty.. Only dust was left."

He falls to his knees and stares at his reflection in the water. His tears fall into the water and his reflection ripples and changes. Chara takes his reflection's place and he screams, throwing his hands into the water, "I hate you!"

He keeps splashing his reflection, which remains Chara, "I hate you! I hate you! I hate you! I hate you! I hate you! I hate you! I hate you!"

He screams and cries, glaring at his returned reflection in the rippling water. He shudders, "I hate you.."

He stands slowly, wiping his face with wet hands. He takes a deep breath and heads to the right. He comes to a bridge and he starts to head across. He stops when he hears Monster Kid run up behind him, "Hey, wait!"

Frisk turns away from Monster Kid, "You should go home. Your parents are probably worried about you."

"Yeah, but.." the Monster Kid walks towards Frisk, "Undyne said to stay away from you.. You're a human aren't you?"

Frisk nods, "Yeah.."

"I knew it, uh, I do now.." Monster Kid sighs, "I guess.. We have to be enemies now, huh? So, uh, be a pal and say something to make me hate you?"

Tears slide down Frisk's face slowly, "I killed your parents once."

Monster Kid's eyes widen, "Oh, uh.. Yeah.. Th-that'll work.."

Frisk wipes his face and starts walking, "Go home, kid.. You don't want to see what comes next.."

"Okay.." Monster Kid looks worriedly at Frisk and then he sighs, turning back the way he came. He suddenly gasps as his foot slips off the bridge, "H-hey!"

Frisk turns back and runs over to him. He throws himself down and wraps his arms around Monster Kid as child falls off the bridge. Undyne walks onto the bridge and gasps, "What are you doing to him?"

"Undyne!" Monster Kid gasps.

Undyne's spear appears and she runs at them. Frisk groans, trying to get back up while holding onto Monster Kid. Undyne prepares to stab Frisk when Monster Kid cries, "He's trying to save me!"

This causes Undyne to falter and Frisk pulls back, rolling away from the edge. He breathes heavily as he lies on his back, still holding Monster Kid. Undyne walks up and snatches the child from Frisk's arms. Without a word, she walks away with him. Frisk sighs and closes his eyes, I can't believe I forgot he trips there.. After a few minutes, he gets up and crosses the bridge. He walks for a few minutes until he leaves the caverns of Waterfall.

The wind howls and he stands before the mini mountain leading to Hotland. On top of the mountain stands Undyne, as he knew she would. Undyne turns to him and he gasps. Her figure flickers and is replaced with the melting mess that is her determined state. Her skin is melting off, revealing sparkling dust and a hint of bones, and multiple slash marks adorn her enhanced armor and flesh. When she speaks, her voice is garbled and Frisk can't make out a word she is saying.

He wants to look away, the guilt is suffocating him, but he can't move. He stares at her as she talks, but her words are lost. Her spear appears and Frisk screams, gripping his head, "I'm sorry! I'm sorry! I didn't mean to hurt them, I was stupid! I didn't want to hurt you, not really, I promise!"

Undyne's eyes narrow, "What are you going on about?"

Frisk doesn't hear her words through what his warped mind created and he starts slamming his fists against his head, "Please, kill me!"