Disclaimer- I do not own either the Naruto or Bleach series. If I did I would be rich. This idea hit me after I read another one where Itachi becomes a Shinigami. The story came into existence after me and a friend attended an all night lock in at the local online gaming score. This is the result of a tired conversation that I only half remember.
/Captain's Meeting Room, Soul Society/
All of the Captain's had been called to attend an emergency meeting, all that was known about the reasons behind the meeting was that it had been called by Kurotsuchi Mayuri. All of the Captain's had been seated at their respective areas for a couple of minutes when the Captain-Commander walked in. With his arrival the meeting could finally begin.
"You have all been called here today because Captain Kurotsuchi has informed me that he has made an intriguing discovery. He has informed me that his scanners have discovered a temporary rift to another realm of existence. Captain if you will," began the Captain-Commander. With that he sat at his designated seat and let Mayuri continue on with the explanations.
"Thank you Captain-Commander, now as you know I have discovered a rift. What you don't know is that my scanners also picked up that the world held an energy source not unlike spiritual power. When I sent an unmanned probe through I the image I received seemed to be that of a battleground. There were no living life-form's in the area, but there was a soul wandering around that held a rather large spiritual energy level, on par with a vice-captain. What I propose is that we send someone through to collect this soul as the rift will shortly close," lectured Mayuri as he glanced around the room.
All of the Captain's spent a few minutes mulling over Mayuri's proposal, one by one all of the Captain's agreed to the plan.
/Ruined Uchiha Clan Compound, Fire Country/
When Itachi had died he thought that there would be oblivion. He was not expecting to be in the same place as where he died. Sure there was his body lying there on the ground, but looking at it was a bit creepy in his eyes. When he had come to, he found Sasuke gone and that there were to of himself. His body slowly cooling on the ground, and what he assumed to be his spiritual form standing by it. The only difference was that there was a short chain sticking out of his chest. As he studied it, he got the feeling that it was there for a reason, so he decided to leave it alone.
"This is not what I was expecting death to be like, well, I suppose that I will just have to deal with whatever happens. Strange, why do I suddenly feel like I am starving?" were Itachi's thoughts as he decided on what to do next. Suddenly he felt a presence form behind him. He quickly turned around to see a rather youthful looking woman step out of a rift that appeared out of nowhere. Staying true to years of practice, Itachi instinctively reached for a kunai when he realized that the woman was armed with a katana. When he reached his side however he only grasped air. He looked to see that his kunai pouch was gone.
"Hello, young man, my name is Unohana Retsu, can you please tell me your name," asked the woman kindly in a warm voice. Itachi felt that it was in his best interest as for some reason he did not want to anger this woman.
"My name is Uchiha Itachi, can you please tell me what is going on here?" asked Itachi.
"All in good time, however I'm afraid that we cannot linger here for long, if you would allow me to perform a Konso, we shall be on our way," replied Retsu. Itachi allowed her to perform this Konso of hers as he felt that it was his best option. When he confirmed his allowance, she reached for her sword, Itachi instantly became wary, but she made no move to strike at him, she placed the hilt on his forehead and he world faded away into darkness.
After Itachi disappeared, Retsu walked back through the rift which quickly closed after she had also disappeared from this world.
/Soul Society/
When Itachi came to once again, he found himself in what appeared to be the front courtyard of a palace that would belong to a daimyo. He heard a voice calling his name behind him and saw the woman from before, Unohana Retsu he believed she called herself. She told to follw her and all would be explained.
/One Hour Later/
Over the past hour Itachi's situation had be explained to him. He was told of Soul Society and the Gotei Thirteen. He was also told that he would be going to the Shinigami Academy as he had too much potential to go to waste. The explanations had continued until his disease had flared up, thus causing him to vomit up a mixture of bile and blood. Unohana had immediately set about the diagnosing him, but was unable to locate the source of the disease, all she could tell him was that it would stop him from fighting for more than thirty minutes at a time and that he would require monthly check ups at the fourth division barracks.
He was then led to the Shinigami Academy where he was enrolled and was given the number of the room that he would be staying in. When he arrived at his designated room he was surprised to note that he was sharing it with somebody else. They were not in the room at this current moment however the name on the door told him who his roommate was. It read Matsumoto Rangiku.
Itachi's time at the Shinigami academy was relatively the same as his time at the Shinobi Academy. He was once again regarded as a prodigy in all of the subjects that they taught. His experiences in life helped him a great deal. His control over his internal energy also helped him through the academy. He made a few friends among the other students but the one that he was the closest two was his roommate. Matsumoto Rangiku was an attractive girl who had a rather large set of breasts. Her personality was also different from his own, where he was withdrawn and rather cold. She was open and friendly to all she met. At first he did not want to make any friends at the academy as he knew that eventually they would all die, but his plans did not work out. Rangiku had somehow managed to worm her way into his heart.
They both graduated together but they were assigned to different squads. While she was assigned to the tenth division, Itachi found himself serving under Captain Soi Fon of the second division. While he was there he worked his way up the ranks until he was able to challenge the vice-captain for the right to be the vice-captain. The man was a competent fighter, maybe a low Jonin skill wise, but against Itachi, he was a joke. Itachi was able to beat him without releasing his Shikai. Itachi served as the vice-captain for the next thirty years until Aizen's betrayal was made public knowledge.
It was official; Itachi was having a bad week. First a group of Ryoka had managed to break into Soul Society, for the apparent reason to rescue Kuchki Rukia. Then it was revealed that a group of Captains led by Sosuke Aizen had betrayed the Soul Society and had joined the hollows. Now he was acing said traitor alone after he had managed to separate him from Ichimaru Gin and Kaname Tosen.
"Uchiha Itachi, such a pity that you had to face me, you have a lot of potential, but unfortunately you chose to stand in my way, I shall have to kill you now," said the rouge Shinigami, "My zanpakuto is the ultimate weapon. Do you want to know what it does?".
"If you don't mind," replied Itachi.
"Very well, it allows me to control the five senses, I can make perfect illusions, it makes whoever sees the release my unwilling slaves forever and you have seen it, unfortunate for you, don't you agree," said Aizen.
"Illusion's you say, you are very arrogant to believe that illusions shall help you here, my zanpakuto allows me to see through any illusion," replied Itachi in an emotionless voice.
Aizen then felt a small slither of fear in his heart, he may be one of the most powerful captains alive at this point in time, however he did rely on his illusions a great deal. He was forced out of his thoughts when he saw Itachi release his zanpakuto.
"Spin, Sharingan," cried out Itachi.
Aizen saw that Itachi's katana had changed into a large war-fan that was chained onto a scythe. However that was not the only change, his eyes, which were formerly a dark grey were now a crimson colour with a black pin wheel spinning where the iris should be.