Disclaimer: I had this idea running through my mind for a while and so I have decided to write this Ben10/Guyver crossover, obviously. This is a Gwen-OC fan fic as Kevin and Ben pairings with her aren't really my thing, actually Gwen-Kevin pairings aren't my thing. I've posted this fic in both Ben10 and Guyver categories as you can obviously see again. Since the Guyver is an alien device it sort of fits with the Ben10 theme. I hope you enjoy. Oh one more thing, I don't exactly know how old Ben and Gwen are in the series so I'm just assuming that they're 10 years old and I'm making them older for this fan fic. Might contain course language.

Another quick thing. The mistreatment of women appals and sickens me. Such as women being sold into prostitution to pay off family debts, being used as playthings for other people's amusement, women being used as hostages, assaulted, raped, stalked, murdered and underage girls being sold off to men for money. Any man who sexually assaults a woman should be castrated as death is just giving them a quick way out, it's better to have them live the rest of their lives knowing they can never have sex again.

But that's just my opinion.

"Speech"

'Thought'

"Phones, etc."

My Bio-boosted Boyfriend.

Four years after Gwen Tennyson's summer adventure kicking alien butt with her dooface cousin Ben and her Grandpa Max had quietened down ever since Ben's ability to go hero using the Omnitrix became public knowledge. With less alien's to battle Gwen was able to focus on being a teenage girl, during junior high Gwen's body had gone through some anticipated changes, according to her mother. She had grown at least two heads in height, gotten more feminine curves and her bust size had gone from her flat A-cup to modest 34b, she also kept her hair short because she liked looking younger. Aside from her monthly period which she thought was totally unfair since guys never bled once a month, Gwen was also getting into beauty products and more girly clothes and underwear while balancing her martial arts classes, school and learning her spells from Charm-caster's book. She even became interested in one of the older boys in their school, a cute looking basketball player called Roy Mustang and had been going out with him for several months. Ben who was again able to turn into his aliens at will had warned her that most sports players only had girlfriends because it got them more attention, and they expected their girls to spread their legs on command. Ignoring Ben's advice Gwen agreed to go to a party with Roy his team were having for the win against another school, and since his friend had a swimming pool, swimwear was compulsory. Fortunately Gwen had bought a new bikini during a recent shopping trip with her girl friends and was waiting for an opportunity to wear it as summer was a few months away.

"Gwen I'm telling you this guy only wants to get into your panties," Ben said waiting outside Gwen's room for her to change.

Ben was going to this party as his friends had invited him along and he wanted to get away from his homework for one night, but he was roped into giving Gwen a lift since she was going as well. Even though he could stay alien for as long as he wanted, Ben had gotten a driver's licence so Grandpa Max had built him a car with a holographic driver for when he had to kick butt.

"Will you give it a rest Ben? Roy has been a complete gentleman since we've been going out," Gwen called back through her door. "And anyway why do you care so much?"

"Duh, because you're family Gwen, I won't let anyone hurt my family even if it's my geeky cousin. So trust me when I say Roy is only acting nice so he can get some action, I've seen the way he looks at you when your back is turned," Ben pressed, know it was useless to argue at this point but still tried to convince her.

"Look Ben, I appreciate you looking out for me but I do have my magic remember. So if and I stress the word if Roy tries something, I'll just blast him away from me," Gwen replied, opening her door. "So how do I look?"

Ben couldn't help think that his cousin looked attractive and her attire now proved that. She was dressed in a short sleeved light blue top with a low neck line that revealed the tops of her breasts and the straps of her sea-foam green bikini top which tied at the back of her neck and a darker blue plaid skirt that ended mid thigh. On her feet were sandals with straps that wrapped around her ankles and a bag in her hands that Ben assumed was a towel and underwear to change into after she had finished swimming.

"At least you're a conservative dresser," Ben said, making his way down stair to his car.

"You used Grey Matter to study for your driver's test didn't you?" Gwen asked as they climbed into Ben's RX-7.

"No, this time I actually studied properly without using the Omnitrix. I'm more responsible than I was four years ago," he replied starting the engine.

The Party.

It turns out that Roy's friend lived several houses away from a large park but Gwen wasn't here for the outdoors, she was here to enjoy her boyfriend's company with other teens from school. The house itself was pretty big with a huge backyard containing a ten metre long pool and hot tub which Ben guessed would have teens making out all night considering it was a Friday, though both Tennyson's had to be home by eleven. There was a lot of noise coming from inside from all the other occupants and loud music blaring from what Gwen suspected was a very large sound system, there were some teens hanging out on the front porch just to get some fresh air or mostly just to talk amongst themselves without having to shout over the music. After getting out of Ben's car Gwen raced over to Roy who had been waiting out front for her and jumped into his arms, giving him a quick kiss as they hugged.

"Glad you could make it Gwen," Roy said, keeping his hands around her waist.

"Hey I wouldn't miss my first real party, just be glad it's a Friday or my parents would have made me stay home," Gwen replied, batting a hand away that tried to sneak under her shirt. "Uh uh, no going under clothes remember? You'll have to wait until we hit the pool,"

"S'ok babe, I can wait," Roy answered, hiding the disappointment in his voice.

"How's it going Roy?" Ben asked, just having finished parking his car. "Gwen still not letting you get under her clothes yet?"

"Yeah but I can wait," Roy replied, putting an arm around Gwen's waist. "Come on, babe, I'll show you where you can put you bag,"

A few hours into the party Gwen had spent most of the time dancing with Roy, eating the available snacks and helping herself to the strictly non-alcoholic drinks. After excusing herself to use the bathroom Gwen came back minus her shirt and skirt with her towel in one hand.

"Wanna go outside for a dip?" she asked, noticing his eyes were ranking over her bikini clad body. "Keep drooling and you can forget about kissing me for a whole week,"

"Sorry babe, just didn't expect you to looking so sexy in your bikini," Roy replied, retracting his tongue into his mouth. "Anyway I don't have anything to change into so I can't go swimming with you,"

"That's ok, you know where I'll be if you need me," Gwen answered, heading for the back door.

Outside.

"Hey Ben isn't that your cousin Gwen," one of Ben's friends Alex asked, where he and his other friend were sitting on the back porch. "Dude, she's got a smoking body,"

Ben looked up from his drink to where his friend was looking, sure enough there was Gwen walking calmly to the fenced in pool wearing her sea-foam green bikini with a towel in her hand. She was easily ignoring the stares from the other guys as she strolled through the gate and draped her towel over the fence beside many others, a few of her friends were already swimming around and called for her to jump in.

"Don't you already have a girlfriend?" Ben asked suspiciously, sipping at a cup full of punch.

"Yeah so what? She's not here so I can ogle any girl I want, even if it is your cousin," Alex said, not taking his eyes off Gwen even as she dove into the pool.

"Too bad she's dating Roy, I'd ask her out right now if she weren't," Ben's second friend Tom added, looking between Gwen and the other swimsuit clad teen girls in and around the pool.

"Remind me why you guys are my friends?" Ben wondered out loud, ignoring their cries of protest.

In The Pool.

"Hey Gwen, I think your cousin's friends are drooling over you,"

"I'm not the only one they're drooling over, Julie. Or haven't you noticed how Ben keeps gazing at you during class?" Gwen teased, her dark haired friend's cheeks matching the colour of her pink neck loop top bikini. "I know there are tones of girls who fawn over him but he turns them all down because all they want is more popularity. All Ben wants is a normal girl who doesn't care if he can go alien or not,"

"And just how would you know all this Miss Gwen Tennyson?" Gwen's other friend Chloe asked, wearing black bikini with bright green outline.

"I sit two seats behind him remember Chloe? I see him looking over at Julie when he's meant to be paying attention to the teacher," Gwen replied, enjoying the way Julie's face deepened in colour. "Too bad Roy isn't in our class,"

"If he was you wouldn't be getting such good grades, cause you'd be too busy drooling over him," Julie laughed, getting Gwen's face to redden significantly.

"Hey Gwen!" Ben called from the other side of the pool fence.

"What do you want dooface?" Gwen asked, slightly peeved at her cousin's interruption.

"Just thought you should know I saw Roy taking one of the cheerleaders upstairs and his hand was on her butt and everything," Ben replied, sneaking glances at Julie who blushed and gave a shy smile. "He stopped long enough to shove his tongue down her throat, and I'm not the only one who saw it. Everyone inside was cheering him on. Go and see for yourself if you don't believe me,"

"You know what? I will, but I refuse to believe he'd pick some cheerleader over me," Gwen growled, pushing herself out of the pool and grabbing her towel to dry off as she made her way back to the house. "So why don't you play with Julie while I'm gone?"

"Come on in Ben, the water's fine," Julie said nervously, a massive blush staining her cheeks.

"Yeah, uh. I guess..., I guess I will," Ben replied just as nervously.

Despite the loud music Gwen was able to ask a few people if they had seen Roy go upstairs with someone, and worst yet Ben seemed to be right, they all said the same thing. Roy had taken a hot blonde cheerleader upstairs for some fun, not wanting to believe them she rushed upstairs pressing her ear to every door listening hard for Roy's voice. Aside from moans and groans from other perverted teens doing who knows what in her opinion, it didn't look like he was in any of the spare bedrooms. Passing the toilet Gwen heard a muffled male groan that sound distinctively like Roy, pressing her ear against the door she listened carefully for confirmation.

"Oh yeah babe, suck it. Yeah just like that,"

Not wanting to believe what she was hearing Gwen used her magic to silently open the door, what she saw made her gasp loud enough to be heard. There sitting on the toilet was Roy with his shorts down at his ankles and a blonde cheerleader minus her top bobbing her head up and down in his lap, and he was enjoying it.

"Roy?" Gwen asked in disbelief.

"What the hell? Gwen? What are you doing here?" Roy demanded, quickly standing up and retrieving his shorts. The blonde groaned in disappointment at the interruption as she covered her chest with her top.

"I should be asking you the same thing!" Gwen shouted. "What you doing with this bimbo when we're going out? I thought you loved me,"

"Yeah well since you weren't putting out for me, I couldn't keep pretending to be nice forever you know," Roy shrugged casually.

"You mean you only went out with me so you could get into my panties? But I'm underage," Gwen protested.

"What can I say, I like younger girls," Roy smirked, wrapping an arm around the blonde's waist. "Sorry Gwen, you're a nice chick and all but a guy has his needs,"

"YOU STUPID JERK!" Gwen shrieked, bolting down the hall with tears staining her eyes.

"Now where were we?" Roy asked, closing the door as he relieved the blonde of her top once more.

Disclaimer: As you've noticed there was no appearance of the Guyver in the first chapter, but it will show up in the second. I would like to hear suggestions for thing you might like to see happen when Gwen runs into the Guyver and when Ben shows up. Right so leave a review and I'll get back with the second chapter.