"Oh? Captain Unohana will substitute at the academy?"
Gusion was surprised.
Tessai nodded, "Of course. Many Gotei captains teach here each year, and since Squad Four needs healers, Captain Unohana often comes to teach—she's scouting future Squad Four members."
He glanced at the students practicing Hadō and continued, "Actually, I mainly teach Hadō, and share some Bakudō tips. Kaidō is a separate elective, usually taught by Squad Four officers or Captain Unohana herself."
Gusion understood—Kaidō required fine skill, and few were talented at it. Most young students aspired to fight, not provide backup.
That's why Squad Four always struggled to recruit; Kaidō was an elective, and those who mastered it usually joined Squad Four.
…
After class, Gusion and Aizen had a satisfying meal before returning to their dorm.
"Sōsuke, do we need to apply in advance for electives?"
Gusion asked—he'd transferred in, but surely they should give him a schedule to pick electives from.
"No need. There are many electives at Shinō Academy. You can just attend, but to get credit, you need to pass the exam at the end. The results go on your record for squad recruitment."
Aizen explained. "Are you interested in Kaidō?"
Gusion nodded, "I am."
"To enjoy fighting even more? You love battle, don't you?"
Aizen felt he understood Gusion—a peerless genius, but also a straightforward, battle-loving brute.
He didn't dislike Gusion. With such a talented roommate, life was much more interesting.
"Sōsuke, don't you find fighting fun? I think you'd make a great opponent."
Gusion smiled. Aizen had hidden his strength, and on the surface, their spiritual pressure was the same—both level 17. Aizen said he'd started at 19 and trained up.
But Gusion suspected Aizen's real level was much higher.
"Gusion-kun, you flatter me. I'm not your match in Zanjutsu or Hakuda, nor do I have your Kido talent."
Aizen said, then changed the topic, "By the way, I see you already have your Asauchi. Though you haven't had Zankensoki class yet, I can teach you some basics about Zanpakutō and increasing spiritual pressure."
"Oh?"
Gusion perked up. "Please teach me, Sōsuke-sensei."
Aizen smiled, "No need for 'sensei.' I only know a little—just some preview before class."
He then explained Zanpakutō basics and spiritual pressure training.
Aizen's motive was simple: he didn't dislike Gusion; in fact, he liked having another prodigy as a roommate. It couldn't hurt to befriend him. If Gusion became stronger, it might help Aizen's plans.
Aizen also wanted to see if Gusion was truly an all-round genius—would he also excel with Zanpakutō and spiritual pressure?
Aizen was a good teacher; Gusion found his lessons easier to grasp than the day's official lectures.
First, on increasing spiritual pressure: since Shinigami are made of high-density reishi, raising spiritual pressure means increasing that density. This can be done through a good diet, absorbing ambient reishi, or physical training.
Yes, even physical training helps—because a Shinigami's body is their soul's density.
But Aizen didn't use that method. He had strong reishi control, so he mainly absorbed free-floating reishi from the air, refining it into his soul.
Aizen's theory matched Gusion's thoughts from reading the manga; for example, Kirio Hikifune in the Thousand-Year Blood War arc said eating food infused with her reishi could boost spiritual pressure.
In this world, Hollows also increase their spiritual pressure by devouring others.
In summary, increasing spiritual pressure is about improving the cohesion of reishi.
That's why Aizen's spiritual pressure was so strong—he had high innate potential and trained quickly.
There were also ways to rapidly boost spiritual pressure: Zanpakutō release.
But not all Zanpakutō grant an increase—most don't. The feeling of increased pressure on release is an illusion; the output just changes.
For example, if a Shinigami's base pressure is 100, before release he can output 5 at once; after Shikai, maybe 10; with Bankai, 40-50.
Some Zanpakutō, though, truly increase pressure on release—like Ichigo's or Kenpachi's.
But these are rare, and usually, the boost isn't dramatic (Ichigo is an exception).
Still, mastering Shikai or Bankai is a huge leap in strength.
But learning Shikai isn't easy; you need a certain spiritual pressure—level 17 is just the threshold.
Usually, only seated officers (who have at least level 10) master Shikai.
The higher your spiritual power, the easier it is to resonate with your Zanpakutō, since this reflects the depth of your soul's development. In essence, Shikai is an expression of the Shinigami's soul.
In short, an Asauchi is just a blank blade—only by infusing it with your soul does it become a true Zanpakutō.
The Zanpakutō's abilities reflect the Shinigami's soul—almost like a manifestation of their essence.
"Sōsuke, you're the top student here—have you learned Shikai?"
Gusion asked, curious for Aizen's reaction.
Surprisingly, Aizen, who usually hid his strength, actually nodded and smiled, "My Zanpakutō is Kyōka Suigetsu, a water-type blade. It can use mist and water reflections to confuse enemies and make them attack each other."
He sat cross-legged on his bed, stroked Kyōka Suigetsu, and looked at Gusion. "Gusion-kun, would you like to see my Zanpakutō?"