Sans POV:

To say Alphy is terrified right now would be a big understatement. The moment I teleported me and Vanny here, Alphy screeched in horror before I rushed the crazy into the cage. It wasn't a perfect holding cell per say. Alphy's did only have a few minutes to put this all together before I came here. It is a simple barrier magic with a glass front in order to see into the cell. It is made of the strongest materials available in all of the underground. It wasn't easy getting her there, especially once she threw the contents off Alphy's desk making a huge mess on the floor. But she was still recovering from the fight, so in the end we got her in without anyone getting hurt.

But our 'guest' here is not being so cooperative. She has been kicking at the wall and shouting for minutes now. Hell, she has even drawn a picture of her own mask on the wall! I don't even know where she got the marker from, but the smile on her face when we noticed certainly was of victory. Luckily Alphy's dedication is so great it doesn't seem to be distracting her as she works tirelessly on her computer. On it is a picture of the human soul, so far, it's being analyzed. I thought I couldn't be anymore unnerving but when Alphy zoomed in on it, I felt a chill run down my spine. I don't know how Alphy's got the backbonefor this.

"This just doesn't make any sense! A-ccording to this… her soul should be perseverance. But whatever this stuff is on it, is acting like a parasite."

"how so?"

"It seems the soul itself is irritated by its presence."

"will it take long to analyze? the sooner we compute this information, the sooner we can get to the bottom of this."

"It will take some time. You… can go… I'll stay here and work on this." I don't feel comfortable leaving Alphy alone with a psychopath. But I trust her to get it done, plus I can't leave the kids hanging. I still have a hang out to go to. I put Vanny's mask on Alphy's desk as I teleported to Waterfall.

Gregory:

So far Waterfall has been different like all the other areas have been. At least it's not so cold here like it was in Snowdin. Shortly after we left Sans, we saw Papyrus talking to someone in armor. I think he said her name was Undyne. She is scary as hell. She almost caught us a few times, but we managed to escape. Eventually Sans showed up again and we went to Grillby's with him. I asked him what happened to Vanny, and he said that she wouldn't be bothering us. After that we went to Papyrus's house and after hanging out with him, he gave us his number.

That monster kid we saw in Snowdin has been following us as well. For some reason they don't seem to know that we are humans. I guess many of them have never seen humans before, if what they were saying about the barrier is true then they must have been down here for ages. Either way after a little while they eventually found out, they tried to insult us, but it was not even close to being bothering. It's like many of these monsters don't even know how to be mean, not that it hasn't stopped them from attacking us!

In the end they couldn't be mean to us, and as they were leaving, they tripped and were about to fall off the bridge we were on. At the same time Undyne was at the other side. Even though it was terrifying, me and Frisk didn't hesitate in saving them. Undyne left after monster kid stood their ground against her. I guess she didn't want to go through them forcefully, but I could have sworn that she was surprised that we saved monster kid.

Now we are standing above us on a hill is Undyne. She is waiting for us to continue forwards before she attacks. She no longer has her helmet on, revealing that she is some sort of fish monster. Frisk has saved so even if we lose the fight the first time, we will just continue right from this point. It still feels weird to think about dying and coming back earlier as if nothing even happened. But it's definitely a useful thing to have.

Looking over at Frisk they nod. We both know it's time to face her. Taking a steep forward Undyne's grin widens as she readies her spear.

"That's it, then…! No more running away! HERE I COME!" I barely have time to scream before she leaps down at us. We enter a battle as she stands, spear in hand ready to tear us apart. Our souls are now green?! Which probably means this will have some sort of effect, just like when Papyrus turned our souls blue. Undyne throws us both a spear surprisingly. I guess she would like a challenge, instead of just having us be destroyed by her attacks.

Undyne attacks as we block using the spears. She seems impressed by it as she explains that since our souls are green, we can't run away from the fight. It's our turn now, I pull out by Fazer Blaster and aiming it right at Undyne's eye I pull the trigger.

"WHAT THE HELL?! YOU LITTLE BRATS, YOU'LL PAY FOR THAT!" Her attacks this time are less coordinated as some miss us all together.

"Cowards! From what I heard of humans they are supposed to fight fair! I will shatter that thing to pieces once I crush you!" Some of her attacks hit us this time as both me and Frisk yelp in pain. We are so focused on the fight that we barely even notice that our souls are back to their usual colors. We exit the battle as we begin to run. Luckily, I was used to it back in the Pizzaplex. Running from murderous animatronics can give someone a workout to say the least. Undyne seems angry as hell though as she curses us out as she gives chase.

Turning around I once again aim the Fazer blaster at her face and fire. She once again curses as her fist slams against the wall causing rock dust to fall. She is quick to recover though as she charges at us and once again our souls are made green. She looks even more pissed off than before.

"For years we dreamed of a happy ending…" I almost get hit as her attacks speed at us.

"You two come along and bring her! She has already taken countless innocent lives. The only reason I am focusing on you two wimps is because I can't find her!" After what feels like an eternity, we manage to escape her again as we continue running Papyrus even calls! To my surprise Frisk and Undyne stop in their tracks. I am already fifteen feet ahead of them when I notice. Undyne seems shocked that Papyrus is calling in the middle of a battle, while Frisk see's to just be stopping to be polite.

As the chase countries I keep firing the blaster at her as Frisk catches up. I also notice the area is getting hotter. This is the exact opposite to how Snowdin felt, where it felt freezing over there here it feels like it is a thousand degrees!

Running up ahead we see Sans sleeping at a station. Undyne notices this as she turns to look at him in frustration. This gives us time to run ahead. Undyne is behind us though, but she seems to be getting slower. As we reach the end of the bridge.

"Armor… so… hot… But I can't…. Give up…" She manages to take a few more steps before collapsing. I take a deep breath exhausted from the running. I can't believe our luck, it's a good thing we are fighting close to here and not at the beginning of Waterfall. I start walking ahead expecting Frisk to do the same. But turning around I gasp as I see Frisk near a water cooler with a cup in hand.

"Frisk! What the hell are you doing?!"

"She's passed out. She needs water." I rush over hoping I can get to Frisk in time, but it is too late. They pour the cup of water onto Undyne as she slowly starts to get up.

"CRAP! RUN!" But to my shock Undyne doesn't have the same fighting energy she had before. She looks confused as she looks around then back at Frisk with the empty cup in hand. Slowly she turns around and starts walking away, still looking shocked and confused.

"Frisk! What the hell were you thinking?!" They look at me with a smile.

"I know that she was trying to kill us, but I couldn't leave her like that." I sigh. Even before I asked them, I could already tell what they were going to say. Is there anything Frisk wouldn't do?! Even though Undyne could have continued trying to kill us, they still decided it was worth the risk of helping her. Even if this was the first time Frisk was doing this, I would bet they still would have done the same thing.
"I know you are just trying to help others. It's just crazy to see you help the person who was trying to literally harvest souls just a few minutes ago." Frisk laughs.

"It's just a trait of mine I guess." Even through my frustration I can't help but smile. Frisk is sometimes too nice for their own good. But it's not like they didn't know what was going to happen. But still they have not given up trying to befriend Vanny even though we just showed up. I still can't understand them, but I know for sure that they mean everything they do.

We continue up ahead, there is some sort of laboratory. To the left of us there are two monsters in armor blocking the path. To the right there is surprisingly a river. There is a boat pulled along the bank, with a hooded figure standing next to it. Why there is a river in this type of environment is still mind boggling.

"I know this is going to sound crazy. But like Papyrus said, we should go and meet with Undyne." My eyes widen as I think back to her murderous smile as she sent her spears at us.

"WHAT?!"

"She won't hurt us. Trust me, and it will be fun." Even though my survival instincts are screaming at me to say no. I reluctantly nod my head yes. If Frisk says it's safe, I'll believe them. But I have never gone out of my way to find danger. In the Pizzeplex I only ever went into dangerous areas to help with my objectives. To go into danger unnecessarily is alien to me. But if it means making Frisk happy, I guess I can do it this one time.

We walk towards where the boat is and surprisingly the person agrees right off the bat to take us. Their voice sounds nonbinary, and the hood is blocking their face from view. Whoever they are, they have a cheerful personality. As we ride in their boat, they say something out of nowhere.

"The princess is lost in the darkness. Her quest unfinished, will she purge the darkness within herself?"

"What?" I look up at them surprised. What could a princess have to do with anything? We just arrived at Waterfall though so there isn't enough time to think about it. We step out of the boat and Frisk waves goodbye to the River Person. That is when we start making our way to Undyne's house.

Author's Notes:

Gregory and Frisk are going to hang out with Undyne. What will Alphy's find out about Vanny's soul?