One Month later , District 1, East Rukongai
A young man looks mid twenties with a spiky black hair slightly messy with his golden yellow eyes exude strength, making him appear intimidating. He wears coarse cloth and a sword old, broken was hung on his waist, his expression is serious walking through the clean streets of District 1 in the East Rukongai. The streets are well-kept, homes are solidly built, and there's minimal crime. Many nobles or well-off souls settle here. The environment feels peaceful, resembling a small, organized town or even a suburb unlike the chaos-ridden outer districts.
People here rarely experience hunger, violence, or the lawlessness common in distant districts. Reishi (spiritual particles) concentration is high and stable, making it easier for spiritually aware souls to live comfortably. To the young man, these surroundings felt like another world, completely unlike the forsaken place where he had awakened.
This young man is Itsuki Hakuto who woke up in District 76. As he made his way down the streets, his mind wandered back to the journey that led him here. It had been a month of relentless travel, from the dangerous outer districts to the heart of Rukongai. Due to his luck or some thing he didn't encounter any hollow during his journey. He had, however, stumbled into groups of bandits who sought to rob him. Though he had never received formal training in combat, instincts guided his every move. His determination to survive, coupled with raw reflexes, was enough to put the thugs down. Even so, the bitter memory of the first Hollow he saw attacking weighed heavily on him. He remembered the helplessness, that sharp hollowing ache of powerlessness, and he swore to himself never to feel it again.
That resolve had brought him here, to this district, in search of the Shin'ō Academy also know as Spiritual Arts Academy, sometimes called the Shinigami Academy. It is an institution founded roughly a century ago by Genryūsai Shigekuni Yamamoto. Located in the Seireitei, the academy trains Souls with spiritual powers for each of the three military arms of Soul Society (Gotei 13, Kidō Corps, Onmitsukidō). the Academy was the foundation of Soul Society's military might. Itsuki knew that if he ever wanted to grow strong enough to protect himself—and one day, perhaps others—this was the only path forward. He had no illusions of what the future held, but for now, all he desired was the strength to never be left powerless.
There was only one problem: he had no idea how one even enrolled in the Academy, let alone if he was qualified. With that thought haunting him, he found his way into a small inn. The place was warm, filled with the quiet hum of conversation and the scent of tea. Itsuki ordered a cup, sitting near a corner table as he contemplated his next move.
When the tea arrived, he passed the waiter a few coins. After a brief pause, he slipped an extra coin across the table and asked, "Do you know where the Shinigami Academy is located?"
The waiter's demeanor shifted at the sight of the tip. With a cheerful nod, he replied, "If you're looking to enroll, head east from here. Outside the Seireitei gates, you'll find tents where they're conducting entrance exams. You can check in there."
Relief washed over Itsuki at the words, he had been prepared to travel much farther. So the Academy wasn't far—he was closer than he had dared hope. Thanking the waiter, he stood, finished his tea in one steady motion, and stepped back into the bustling streets. Itsuki Hakuto adjusted the sword at his side, his heart steady but burning with anticipation, and began walking east.
Reishi (Spirit Particles) composes the spiritual bodies of Souls, including Hollows and Shinigami, and everything in Hueco Mundo and Soul Society. Reishi is invisible and intangible to mortals, with the exception of spiritually aware ones.
Reiryoku (Spiritual Power) is a power aligned with the spiritual sensitivity and willpower of the user. It is used by Shinigami and other spiritual beings to provide power for their various abilities. Every spiritual being and every Human has a certain amount of Reiryoku. If this amount is higher than a certain degree, it grants the person superhuman abilities. Those with such an above-average level of Reiryoku are very rare among living Humans. There are power levels even among the Shinigami's according to how much Reiryoku one possess. For Example the Reiryoku between the low ranking Seated and Non Seated Members of the Gotei 13, Lieutenant rank and Captain rank Shinigami. Reiryoku is most quickly increased when a Soul is in a life-or-death situation, so the more you battle, the more you win and the more Reiryoku would increase.
Reiatsu (Spiritual Pressure) is the physical force/pressure that a person's Reiryoku creates when released. The difference between Reiryoku (Spiritual Power) and Reiatsu (Spiritual Pressure) is simple: Reiryoku is the amount of energy a being has stored within their body or soul, whereas Reiatsu is the pressure that a person's Reiryoku exerts. In other words, Reiryoku is potential while Reiatsu is energy in use and can be sensed by other spiritually aware beings.
When two spiritual beings collide, the side with weaker Spiritual Pressure will get hurt. Ex: When Ichigo Kurosaki fought Captain Zaraki Kenpachi, the Captain opened up the chest area of his shihakushō and ordered Ichigo to cut him. When attacking with all his strength, Ichigo found Zaraki uninjured, while his own hands started bleeding. As his sword's power is highly concentrated for the purpose of killing, the Spiritual Pressure that Zaraki subconsciously releases is much, much stronger. In this way, a Shinigami with a greater amount of Reiatsu can use their own Reiatsu to harden their skin and effectively protect themselves from attacks. Once Sousuke Aizen's said, "Shinigami battles are battles of Reiatsu; if one combatant possess a significantly greater level of Reiatsu, then the other's abilities can be overcome".