A/N I don't own avatar
Do-San had captured the Northern water tribe. Dead bodies were strewed out on the ground from the battle. The destruction was massive. He had his own team of waterbenders re-build the structures for another attack because he knew that there would be a counter attack.
He walked to the spirit oasis and entered it. He stood in front of the small pond that contained the two coy fish that were the ocean and moon spirits. The old man pulled out a scroll from his pocket and opened it. He read the chant out loud with his hand extending out over the pond. Half way into the chant the pond started to glow. It continued to glow after he had finished the chant. He looked satisfied with what he had done and left and waited for the counter attack. Then he would unleash his ultimate weapon.
Hei-Bei stopped outside of Koh's cave. Aang dismounted and took a deep breath. He let all of his emotions leave him. He walked into the cave and waited. In the blink of an eye Koh appeared. He stood face to face with Aang. He then started to slowly circle around the avatar. "Well, if it isn't my good friend avatar Aang. I'm impressed at the success you have achieved." He said tonelessly. Aang was surprised at what the spirit had said, though, he did not show it.
"Why are you impressed with me?" he asked the face stealer.
"Well your achievements have become legendary." He answered "You helped save the ocean and moon spirits. You defeated the fire lord. You even defeated the pirate emperor. Although I hear it did not end happily." He finished.
"What do you mean?" Aang asked in the same curious, but emotionless tone.
"I know exactly why you are here. You are looking for your wife, Katara. I will help you. She is in the yang spirit world." Koh explained to him.
"The yang spirit world?" Aang asked confused at what the spirit had said.
"Yes, let me explain." Koh told Aang about the spirit world and what it contained.
"So Katara is located in a separate realm of the spirit world?" he asked.
"Yes, but there is another thing: the North Pole has been attacked. I don't know who is in charge, but you must go now. Find Katara and get back to the physical world and stop this threat. Bring balance to the world again." Koh said to him before slipping back into the shadows. Aang left to get Hei-Bei and ride off to the yang spirit world.
Zuko had about seven ships under his command. Standing to his right was Mai and to his left was Ty Lee, behind him stood Iroh, who also insisted on coming with him. Zuko hoped that the fleet he had would be enough to retake the North Pole. They sailed at full speed; he could only hope Sokka was still putting up a fight.
An hour later they saw smoke from a ship ahead of them. Looking through the telescope, Zuko identified Toph and Kuzon on the ship. Once they sailed closer, a plank was sent to Kuzon's ship. "It's nice to see you again, Kuzon." Zuko said to him shaking his hand.
"Likewise." Kuzon said back.
"I take it that you received Sokka's message." Zuko continued.
Nodding he replied, "Yes, I did."
"Join the fleet" Zuko commanded.
Bowing, Kuzon left to talk command the ship. Once the ship had joined formation, they sailed off for the Northern water tribe.
The yang spirit world didn't seem too much different from the yin spirit world, either way; Aang didn't want to stay much longer. He searched thoroughly for Katara, until finally he saw her. He jumped off Hei-Bei and ran for her. He threw his arms around her. Katara seemed to be crying, "Oh, Aang. I'm so glad you're here," she said, "This place is so scary, let's just get out of here."
He nodded and turned to Hei Bei, "How do we leave?" he asked. They followed the spirit to what seemed to be a gate; the same one Aang had used to return to the North Pole years ago. Hei-Bei transferred them back, and they found themselves at the spirit Oasis.
They saw an old man, whose hood covered his face. "Ah, the avatar," he began "I'm impressed to finally meet you here. Unfortunately, you won't be around for much longer." He outstretched his arm over the pond, where the two coy fish swam, and chanted something in some ancient language. As he did the pond flashed a bright white, as the water flowed in a great swell to the front of the Northern water tribe. As it rose from the water, Aang identified it to be the ocean spirit, but Yue was in the middle like Aang had been when he worked together with the spirit. There was something wrong though, Yue's dress was not a brilliant white, but dark. Her eyes also contained the jet black color. It took a moment to realize that the old man had summoned the yang spirits of the moon and Ocean!
He and Katara worked as one. Together they ran for the spirit and attacked with shards of ice, but the spirit made little work of it and sent it back at them with twice the force. Aang had to resort to using airbending, obviously fire wouldn't work and there were no rocks for earthbending. Katara stood back and handled the troops that were rounding up the last of the villagers.