Hi everyone. Well, this is my very first crossover and I thought I would try something new. I enjoyed the last Airbender and the Legend of Korra so I thought I'd give it a try. Also, TMNT would be interesting to do. Besides… who hasn't imagined the turtles bending the elements? Anyway, I hope you guys enjoy!

The moment Avatar Korra made the decision to keep the portals open, many changes soon followed. Spirits and humans had not interacted with each other for 10,000 years. Changes were made, battles followed, but the biggest change of all was the physical world.

"Did I do the right thing" Korra had asked her teacher once, and that question would remain with her for the rest of her life.

Spirits and humans had gotten along fine. Of course there were issues and some difficulties, but everyone tried their best to get along. That has remained for 250 years. The avatar, Tang Shen, an airbender by birth, was a prominent bender and had much potential. She had mastered all four elements at age fifteen and mastered the spiritual side at age seventeen. Tang Shen had accomplished so much at such a young age. One day however, she decided to leave and live in Republic city with a fire bender named Hamato Yoshi. Her family was curious as to why she would leave so suddenly.

"Even the avatar cannot be denied love. We are mortal as well."

So there she stayed with her Yoshi and had a daughter named Miwa. One day however, Tang Shen mysteriously disappeared. Miwa and Hamato Yoshi had vanished as well. Only one month after the family disappeared, a fire bending gang named the foot started ruling the underground of the city. They were an unstoppable force. Not even the president could touch them. Sixteen years passed since then, and Republic city was still suffering under the tyrannical rule of the Shredder, leader of the Foot. Unknown to the citizens, they will be saved by unlikely heroes and a new avatar…

In the Spirit realm, there was a small house with a dojo on the side of a floating river. Inside were four unusual beings, even by spirit standards. Four human like turtles that had the ability to bend an element. Currently, inside the dojo, the blue masked turtle named Leonardo was fighting with his younger brother named Michelangelo is wearing an orange mask.

"You think you got this bro… I'm here. I'm there, I'm everywhere!" Michelangelo was taunting Leonardo while they were practicing with nunchakus and katanas.

On the other side of the dojo the other two turtles, Raphael with the red mask and Donatello with the purple mask, were also training with a Bo staff and Sais. Donatello spun his staff before pointing it at his older brother. Raphael for his part merely cracked his neck and put up his Sais.

"Alright Donnie. Put the staff down, and no one gets hurt."

Donnie gave his brother a deadpanned look.

"Uh yeah that's what you said last time Raph. And then you hurt me."

"Yeah, well, last time I would have,"

Donatello immediately began attacking Raphael with the staff. Raph immediately began dodging and attacking back. After a little bit of time, the younger of the two finally swung his staff at the older with his eyes closed. When he opened them, Raph was standing in front of him holding his staff. Smirking Raph breaks the staff. Paling Donnie stared at him.

"Should've dropped the staff?"

"Should've dropped the staff."

Raph the proceeds to beat him with his staff. Donnie surrenders and goes to sit in the corner and wait. Meanwhile Michelangelo was dodging every attack Leonardo was throwing at him.

"You can't catch me son. I'm everywhere. Think you could catch me?"

The blue masked turtle smirked, turned his katana around, and striked the orange masked turtle with the hilt. Immediately, he went down.

"Like that?"

"Good one Leo." Mikey said with a weak thumbs up.

After Mikey got up and sat next to Donatello, Leo and Raph proceeded to spar with each other. After a little bit, Raph flipped Leo over and won the match.

"Yame."

The turtle brothers lined up and waited for their sensei to come in. Soon, a human like rat in a red robe came in and stood in front of his pupils.

"You four did very well today." He commented.

After that, Mikey stared at his teacher with puppy dog eyes.

"Master Splinter. May we please?" He asked.

Master Splinter turned away his head and stroked his little beard. When he turned, all of his sons were giving him the puppy eyes. He sighed. How could he say no?

"Very well. But for one hour only. The butterfly-frogs are migrating through soon and we all know what happened last year."

In a split second, the turtle brothers dashed for their rooms and put on specific clothes for this occasion. A few minutes later, all were outside practicing their bending. Leonardo was in an outfit that had no sleeves and is the color blue. It was made from the Southern water Tribe and Leo was wearing it while was slicing dummies with his water bending. Raphael was in a short sleeved fire nation that was red and orange. It was made from the Fire nation and Raph was wearing it while striking dummies with his fire bending. Donatello was in a long sleeved outfit that was white with green linings. It was made from the Earth Kingdom and Donnie wore while levitating the earth rocks and metal and striking the dummies. Michelangelo's outfit was a simple yellow and bright orange robe. It was made from the Air Nation and Mikey wore it as he bended the air on the dummies.

"This is epic!" Mikey shouted as he finished with the dummies and grabbed his glider and flew in the air.

"You said it Mikey!" Raph agreed as he threw a roundhouse kick and blew up one of the dummies.

Donnie and Leo didn't say anything but smiled to themselves. They barely had time to practice their bending these days. Master Splinter wouldn't let them leave unless the area was clear of spirits and animals passing through.

"Hey guys, check it out!"

All the boys stopped what they were doing to check out what Donnie was looking at. Soon, they saw the fleet of butterfly-frogs heading their direction. Mikey was very interested and was about to glide over when a metal cable grabbed his leg and brought him down.

"No Mikey, We don't want to repeat last year." Donnie explained.

Raph and Leo grabbed Mikey by the arms and dragged him inside with Donnie following.

"NOOOO! They were calling me! I have to"-

Mikey stopped and smelled the air. Apparently, their surrogate father was cooking something.

"Food!"

Mikey broke free of his brothers arms, and used his air bending to run to the dinner table. The others followed and were happy to know that Master Splinter had cooked their favorite noodles and pot stickers for dinner. While they were eating, Mikey had asked Splinter how they were different from both spirits and humans.

"Yeah sensei, why do most spirits say we're different?" Leo had asked.

Master Splinter sighed. The boys were fifteen. It was hard, but he could try to explain things in the best possible way.

"My sons, I found you in the spirit world fifteen years ago after a rat spirit entered my body and left me in this state. You aren't human because you have bodies like the spirits and were most likely born here. However, you are not spirits because you're bodies are physical like a humans and all of you can manipulate an element. Spirits cannot bend but humans do not have the appearance of animals."

The boys pondered on this explanation. It was true. They had lived in the spirit world all their lives. They weren't exactly spirit material. They had never been to the physical realm and never met any humans. The turtles looked at each other. It was obvious that they weren't going to find out what they really were staying here. It was finally time to ask their adopted father the question they wanted to ask since children.

"Sensei, can we please go to the physical realm?" All of them asked at the same time.

Splinter stared at them, face neutral but mind in shock.

"Boys…this is a very serious question you're asking. You've never been outside of the spirit world and are still training in both your bending and the art of ninja. You're only fifteen. The physical world is a dangerous place."

The boys didn't give up. Leo spoke first.

"Sensei I know you're trying to protect us, but we can't spend our entire lives hiding here. Plus, we're benders. We've been self-taught, but we need teachers."

Raph cut in.

"I can't even control my fire for ten seconds. It gets out of control every time I hit our target dummies."

Splinter closed his eyes. His sons were right. They needed teachers and can't stay within the spirit world. With a heavy sigh, he stared at his sons with his answer.

"You may go after the sun has set. Use the floating river to head for the spirit portal in the field of flowers. That one will take you to Republic city."

The brothers leapt for joy. They were finally going to see the physical world. With a few hours until the sun set, all turtles began preparing for their big adventure. They kept their outfits on but brought their weapons just in case.

"What do you think the physical world is like?" Mikey asked to no one in particular.

Donnie answered that one.

"Well, from the books I've read and the science's I studied, the physical world is simple. Rivers flow straight and the landscapes just go up and down. Humans are pretty intelligent and… why am I still talking to you?"

"Don't know. Thought you'd figure it out by now."

Soon, the sun had finally set. Master Splinter gave them one final piece of advice.

"This is a new world you're entering. Use your ninja training to remain in the shadows. And do not make any contact with humans and do not let the spirits know where you are going. They will inform their human friends."

"Hai sensei!" All four replied.

The turtles bowed in respect and left for the floating river. Before anyone jumped in, Leo made a raft of ice for his younger siblings. Soon they reached their destination. All jumped off and ran for the portal. They stopped in front of it.

"So…who's going first?" Mikey asked, awestruck by the portal.

Leo answered.

"All of us, on my count."

Raph didn't look happy.

"Who made you leader?" He demanded.

Soon, an argument started between the two siblings. Donnie just watched on while Mikey stared at the flowers. After a few minutes, the purple masked turtle decided to break it up.

"Guys how long are you gonna keep this up? I'd prefer to see the physical world now."

Both stopped. They looked at their brother and then the portal. Leo went in first, then Donnie, Raph had to get Mikey to go through before he followed suite. When they got on the other side of the portal, all of them were stunned.

"Whoa…"

There were more buildings than in the spirit world. Vines covered every area and lights illuminated through each plant life. Immediately, the boys ran for the roof before any spirit could see them. They ran through the forest of vines and soon, they saw the entire city. It was amazing. After a few minutes of just standing around, they jumped from roof to roof enjoying the scenery. Raph soon spotted a large stadium.

"Hey guys, check it out."

The others stopped to stare at the building. Mikey immediately knew what it was.

"Dudes, I overheard the some spirits talking about that. That's the pro-bending arena. All the cool benders go there and compete for the gold. Well, except air benders…" He said the last part with his head down.

Leo put his hand on Mikey's shoulder. Raph still stared at the arena. It looked like a match was going on.

"Raph…not a good time."

The red masked turtle turned to face his brother. As much as he hated to admit it, Leo was right. They needed to find a teacher to help them with their bending. So then they continued to jump from building to building. After many hours, they decided to head back to the spirit world. Just as they were about to head out, Donnie spotted a couple of humans.

"Guys, check it out!"

They stopped to look at the humans. One of them was a middle aged man with short red hair wearing a business suit. The other was a teenage girl with a red braid and wearing a blue short sleeved shirt and brown pants. Donnie immediately started seeing hearts when he saw her.

"She's the most beautiful girl I've ever seen."

"She's the only girl you've seen." Raph stated.

Donnie only glared at him. All of a sudden, a group of men came out and tried to attack the red headed humans. The girl immediately water bended the one of the men against the wall. One of them immediately threw fire at her face. She then dodged it. Donnie couldn't take it.

"We gotta help her!"

He then pulled out his Bo staff and went down to help. Reluctantly, the others followed. Soon, they appeared behind the gang. Nearly all of the men could bend either fire, water or earth. The turtles fought bravely, Raph attacked with his Sais and Mikey used his nunchakus. They desperately wanted to use their bending, but they promised their father to only stick to ninja training. The other two humans were stunned by this.

"Dad…what are they?" The young girl asked.

"I don't know April, they may be spirits."

While no one was looking, one of the men sneaked up and electrocuted April. She collapsed in pain.

"APRIL!"

Donnie turned and saw the man grabbing the father and another about to grab the girl. Without even thinking, he used his earth bending to hit the man trying to grab her. All the men stopped and stared at the ninja turtle.

"Dude… that spirit can BEND!"

"Let's get out of here!"

Soon, they all fled. Raph tried to make chase, but soon lost them. This was bad. Those men still had the girl's father and said girl was unconscious before them. Leo gave Donnie a hard glare.

"Donnie! What were you thinking?! Not only did you allow humans to see us, but you used your earth bending when we were specifically told not to!"

Donnie saw red.

"What else was I supposed to do!? Let them get captured?"

Mikey interrupted the two before it got worse.

"Um guys, what do we do about her?"

Everyone stopped what they were doing. They all stared at the water bender who was not waking up anytime soon. Donnie picked her up bridal style and offered a solution.

"Let's take her to Master Splinter guys. He can help her."

Soon after, they reached the portal. As they stepped through, there was one thing on all of their minds.

'Sensei is gonna kill us.'

This is a new story for me, so feel free to review. I hope you guys enjoy!