Hey guys it's me with something interesting for Ben 10. It's a crossover with Monster musume with a twist I will make in each chapters. It still has the same characters from the manga and anime but Ben will have a very large harem.

So here is ben's life with monster girls. I own this fic, both shows belong to their respective owners.

Ben's Life with Monster Girls

Chapter 1: The Interspecies Program

Bellwood, 1:00 am

Ben and Room were driving to the plumber base as usual, but Ben was feeling like something was gonna happen.

"Are you alright, Ben?" Rook asked as he saw Ben looking like he was ready for anything.

"I just have a feeling like something's gonna-" Ben was cut when Room slammed the brakes. Hard.

"Ow. What the hell man?" Ben cussed at his partner.

"I am sorry but…" Rook pinged to the road and Ben saw why they stopped: a girl was hurt and on the road. Ben went hero and opened the to get out.

"Ben, what are you doing?" Rook asks as he saw Ben stand over the girl.

"Rook get over here." En called to his partner. Rook went to Ben and saw something weird about the girl: she had a snake tail!

The girl had a red snake tail coming from where her legs should be. They saw that she had been running or slithering from some people and dropped to the road, tired and now sleeping. She had a cute face, with some red scales here and there and had pointed ears. She wore a yellow teared shirt that exposed some of her...assets and she clearly needs food and water.

The two of them were astonished by the girl's beauty until Ben crotched down to see that she had been crying. Ben didn't like seeing a girl cry so he did something really brave or really stupid.

"Rook help me get her in the truck." Ben said to his partner, who looked back to see Ben pick up the girl with his weight. Rook thought what was he doing, but remembered as a plumber, he is there to help those in need and this girl was injured.

Ben was with her, trying to see if she was alright. She was breathing, but was still out of it.

"We go its head to base! Step on it!" Ben told Rook.

"Step on it? Step on what?" Rook asked.

"Just drive back to base!" Ben yelled at him.

"Right!" Rook stepped on the gas as hard as he could. "Oh, now I get it. Step on the gas, meaning 'step on it.' Now I understand."

"Not the best time, Rook!" Ben yelled from the back.

"Right! Plumber headquarters, this is Agent Rook Blonko. I need medical service right away!"

"Medical service for who, Agent Blonko?" A medical officers voice came over.

"It's for what appears to be a half snake alien girl. We are heading to base point now." Rook said.

"Half snake?" The officers voice asked, then came back again. "You mean you guys have a lamia with you?! Are you insane?!"

"What do you mean? And what's a lamia?" Rook asked.

"I'll tell you guys when you get here." The officers voice then was cut off.

'What happened?' Rook thought.

*some time later*

Ben and Rook bright the girl to be examined. They had no idea what she was till the doctor came.

"So, how's the girl?" Ben asked.

"She's fine, but you should know what's going on." The doctor said.

"What?" Rook was the one to ask.

"Sometime ago, the Interspecies Exchange Bill was passed by the United Nations committee to allow liminals to come to the world and experience the rest of the world. There are agents that keep tabs on where liminals live and how they're treated." The doctor said.

"Yes, I remember about that. This happened three years ago." Rook said. "How could I forget?"

"I dunno, but what's gonna happen to her?" Ben asked.

"Well, her agent called and she's gonna try and set up a new place for her, but she won't be here til tomorrow." The doctor said.

"Ok." Ben said.

"Do you….want to see her?" The doctor asked.

Ben nodded his head, wanting to see her.

*5 minutes later*

Ben found the girl she rescued, sleeping peacefully. Her bed was extended to let all of her sleep. He walked up and sat on a chair by her bed.

"What happened to you?" Ben asked her. "Why would someone do this to an innocent girl?"

Then, she started getting up. She moved and loaned as she opened her eyes. She then looked to where Ben was sitting.

"Hello." He said casually. She reacted….casually.

"H-Hello." She said softly.

"How are you?" Ben asked softly. Then he got straight to it. "What happened?"

"I...I was chased out. My exchange family cast me out for being a problem. Then…." She started to tear up. "I was chased. I just slithered as fate as I could, but the forest was so dense, I got hurt along the way."

"Well, it's a good thing I found you. If I didn't, something might've happened." Ben said.

"Thank you." She said, blushing at him. "Oh! I don't know your name."

"Oh. It's Ben." Ben said. "And you are?"

"I'm Miia." The now named Miia said. "As you can tell, I'm not like other people."

"I can tell by the snake tail. But, it's no big deal for me." Ben said. "I meet different aliens, so monsters aren't that different."

"Thank you. You're the first human to say nice things about me." Miia said.

"Well, I'm part alien and I can turn into other aliens, so I get what you're going through." Ben told her.

"Really? That's so cool!" She said. She then saw who was here too.

"What?" He turned and saw a woman in a suit standing behind him. "Uh, Who are you?"

"Names Agent Smith. I'm her CEC." She said. "And you must be the legendary Ben 10, wielder of the Omnitrix."

"How do you…?" Ben was gonna ask, but he was cut off.

"We know everything about anyone. And you're the top hero that everyone knows." Smith said.

"Ok?" Ben said, confused.

"Listen. Her host family is gonna face charges, so maybe we should send her….with you." Smith told Ben, who looked like he found out something about his family.

"Imma Say What Now?!" Ben was flabbergasted. "W-Wait a minute now!"

"Sorry, but that decision is made." Smith said getting on her phone. "Ok, I'll see you tomorrow."

Ben stood there, completely shocked at what just happened. He was gonna be a host to the girl he saved.

'What did I get my shelf into?!' Ben thought. He was in for a new adventure.

*1 day later*

Ben got back home, because he needs to rest after what happened. When he opens the door, Agent Smith was talking to his parents.

"So that's how it works. If you just sing these." She pulled out a form for them.

"Wait. What about Ben?" Carl asked.

"Yeah? What about me?" Ben said, getting their attention.

"Hello, Ben. We heard what happened, and were proud of you for that." Sandra said.

"Yeah, and ms smith here is telling us that we're gonna be a cultural exchange host family." Carl said.

"Yeah, I know." Ben said.

"So?" Smith asked.

"Yeah, I'll win it. It be nice to have a friend here." Ben then signed his name, along with Carl and Sandra, and have it back to smith.

"So with that, you are now Miia' she's family." Smith said. "I'll let Miia get here."

Ben was left with his parents as Miia was coming.

"Well, I guess it's gonna be interesting with a lamia here." Sandra said.

"Yeah, but she needs to know what we know." Carl said. "About our family."

"I told her about me. She was surprised, but I told her about being ridiculed." Ben told his parents.

"Well, it'll be a nice change of face." Carl said. "Come on, let's meet her."

*outside*

Bens and his parents were waiting to meet Miia. Then a van came up and stop. Out from the front was Ms Smith.

"Oh. Glad to see you guys." Smith said. "Well, let's get going."

Miia came from the back of the van as slabs slithered to the Tennyson family.

"Hello again, Ben." She said, blushing a bit.

"Hey, Miia. Glad to see you're better." Ben said to her, making her blush more.

"Well, we'll have to do some construction to her room." Smith said, surprising the three.

"Wouldn't that cost over 100,000 to do?0 Carl asked.

"It's all government payed. You won't pay a thing." She reassured them.

"Well, I've always wanted to redo the kitchen. Maybe…?" Sandra asked.

"Don't worry, that'll be taken care of." Smith told her. Then she turned to Ben. "Now, here's the rule book for what to do."

"This looks like it's heavy." Ben said, holding the book.

"Well, it has a lot of rules but I'll tell you the base three." Smith said. "You can't let her go out alone, so you need to accompany her wherever."

"Ok, but what if I need to head to the plumber base and such? And what about my parents?" Ben asked.

"Well, With your parents here, they can look after her, but she is your responsibility, Mr. Tennyson." Smith pointed out. "What happens to her is on your hands."

"Seriously?!" Ben tried to not think of it, but went on with it. "Ok, ok."

"Next, She can't hurt any humans since she is a representative of her species. If she hurts a human, she gets sent back. Comprende?"

"Yup. I'll hold on to that." Ben said.

"Alright, and the last is important, so you need to follow this one rule." Smith told him. "Mr and Mrs Tennyson, you need to listen too."

"What rule?" Carl asked.

"You cannot, I repeat, cannot….Have. Sex. With. Miia." Smith said, causing the two younger to blush.

"W-What are you talking about?" Ben asked, flustered.

"The bill states that, if you are caught having intercourse with your liminal guest, the guest will be sent back and the host will be sent to jail." Smith explained.

The Tennyson family was flabbergasted. If their son has sex with Miia, he can't be the hero everyone needs anymore.

"Don't worry. I'm not gonna do anything to her. I promise." Ben said.

"Well, if you say so. Just to give a heads up, lamias are all woman, so watch out for her advances." Smith told Ben .

"You got it." Ben said to her.

"Well, with that out of the way, I'll see you later." Smith said, taking her leave.

Ben and Miia, along with Carl and Sandra, walked back inside.

"Well, Miia, welcome to the family." Sandra and Carl said.

"It's an honor. I hoe I learned many new things here." She said enthusiastically.

"Well, I guess nothing else will happen." Ben said, jinxing himself on what he said.

*meanwhile*

A certain harpy was dodging agents of the bill.

"Can't catch me!" She said happily.

"Papi, get down from there!" An Agent said. "This happens every time."

"Could be worse." Another one said.

"Yeah." He turns back to the harpy. "Get down here this instant!"

Hey guys, so this idea popped when watching some episodes of Monster Musume and Ben 10, so I thought it would be interesting.

I'll see you guys later.