Dipper pov.

"Pine tree get up."
I groan and sit up.
"Good afternoon pine tree."

"Hey Bill."

"The tanks are supposed to be drained and cleaned today so your gonna have to come with me and hang out in the pool."

"Ok." I said tiredly.

"Y- ...."
Did he say something?
"Did you say something?"

He chuckled and opened the tank lid. I crawl out into his arms. And he took me down the hall. We went in to a room there was a big pool of water. White marble floors. The pool reflection. Bill walked down the steps. And drops me in. I swim around. at one part the water was deeper. I swim to it and leap out of the water and dive back down splashing Bill in the face. We splashed and played around.
It went on for a few hours when Bill decided to get out. I sat on the edge of the pool with him.

"Lets go take a bath."

"Bath?"

"Yea like cleaning your body."

"....."
".... you live in water of course you haven't had a bath."
He laughs then dries himself off and picked me up.
He takes me out of the pool room into another room not to far away. The room was hot. And streams he placed my in the water. He dropped his swimming pants. I blush as he got in the water.
"You didn't grow a tail?"

"Well yea I'm human. We don't grow tails. Ever."

I grab his leg lifting it up looking down at the floppy thing between his legs.

"Pine tree put my leg down."

"What is it?"
I asked I reached towards it.
"Pine tree wait hold- mhm!"
My hand stroked against it.
"Pine tree stop before you get me hard."

"It can gets hard? Does it feel good?"

He leans head back against the tile.
"Y-yes it can get hard. And obviously feels good."
He grabbed my hands and lifted me up and sat me on the hard floor.
"You saw my mating stick so you have to show me yours." He said.

I blush. I lean back a bit and open a small flap showing my virgin hole.

He touched my cheek and leans in kissing me. My back arched and I lay fully on my back. He slides me back into the water. I was between his legs. I remembered Tad's words. I pull away and lean my head against his.
"I'm sorry. But I can't."
I move off of him
"What why?!"
He asked.
"My hand was already promised. If I don't return to the sea. He'll hurt my Grunkles and sister and destroy my village."

I fiddled with the ring on my finger "I can't put my sister through that kind of pain. I want to stay and you're dear to me. But Tads a mermaid he can walk into the land."

"I'll take you back to your home"

"No I have to go alone. Unharmed unchallenged. And a virgin."

"Pine tree I only want you though." He took my hand into his.
"I know. But we can't. You live on land and I can't stay behind a clear wall the rest of my life.  We won't be able to be together."

"That's right!"
I jump to the voice behind us. A man in purple was standing in the door way he had a sword against the kings neck. Bill grabbed me from my waist and stood up the thing between his legs was hard and twitching against my womb hole. My arms were around his neck.

"Bill. Please put me down." I begged him

"Tad lets make a deal!" Bill shouted.

"Bill it's no use you can't keep me-"

"Sush love. What deal Demon?" Tad stopped me from talking. D-demon?

"I'll give her to you. But her first child will be mine! Or her first child will be yours and I get to keep her."

"Aww but you see. I want her to myself. Her beauty will be mine. Forever! Now hand her over!"

"The deal! Pick!"

"How about this. We let the child determine who gets her. Each of us will sleep with her. If it is my child she will return with me. If she is yours then you can have her. What do you say?" Tad proposed. 

"Pine tree?" Bill looked down at me.

"I'll have to return to sea eventually. I really don't want a child now. But if I must then I will." I said in sadness.

"Alright. It's a deal then." Tad pushed the king out of the bath. And closed the door locking it.
Bill thrusts himself into me. I yelp. He readjusts my body and sits in the water he thrusts into me and groans in pleasure. I moan out with each thrust. He took a breath and we went under water. I kiss him so he can breath through his mouth. My tail wrapped around one of his legs. He thrusts into me faster. I moan into his mouth. He held me closer. He takes a final thrust Cummings inside of me. He pulled out of the water panting. I was pulled out from under him into Tads arms. He kissed me and thrusts himself into my sticky hole. My tail moved off of Bill and around Tads tail. While moaning. He moved against me. I heard Bill get out of the water. Tad cum filled me with his sticky seed. He got off of me. I go to the surface. To see the two boys glaring at each other.
"I want to return home."
They looked at me. Bill nods. A servant brought him clothes and a cloth to dry himself off. I get out of the water and was wrapped in this cloth and Bill picked me up as Tad got out was turned human with clothes.
"Bill what is the meaning of this!?" His step mother yelled.
"I'm leaving again. I'll be back soon."

He took me down to the sea.
"I'll come with you guys."

Tad rolled his eyes nod dived into the water. Bill kissed my lips. I jumped out of his arms into the ocean he followed. I start swimming home. Tad went back to the kingdom. Bill followed me. Bill had a golden yellow tail.
I saw my village in the distance.
"Pine tree slow down a bit!"

I giggle and slow to Bills side. I take his hand and speed with him. Mermaids and mermen were picking up and cleaning my Village. It looked a little trashed but not much.
"LOOK EVERYONE DIPPER'S BACK!"

Everyone was happy they all welcomed me.
"DIIIIIIIIIPPPPPPPPPPPPPPPPPPEEEEEEERRRRRR!" My sister zipped right to me. I open my arms embracing her impact.
"I MISSED YOU TO MUCH. What happened are you mate yet?! Did you runaway again!? What tell me tell me tell me tell me! Ohhhhh who is that siren? He's kinda hot."
I giggle as Bill blushed.

"Bill this peppy mermaid is Mabel Pines. Mabel this is prince Bill of the human world."

"Pines?"
"Human world?"

They looked at me confused.
"Bill my sister. And he's a demon he's my mate also."
They oh'd. Mabel took my hand and pulled me to the shack Bill followed. I was welcomed by Ford Stan Wendy and Soos. I explained to them what happened.

"They made a deal. There's a chance that if the baby is Bills then I don't have to marry Tad. I love Bill. Please don't be mad."

"Well if there's a chance where you can have the mate you want then we're not mad."

I let out a sigh and hug them. Now all we have to do is wait.