"For this problem, you need to set up the unknown first, then substitute it into the equation..." Orihime Inoue patiently explained to Rukia Kuchiki. "Factor out the common term, and you'll get the answer."
Rukia Kuchiki's eyes lit up. "Oh! That's amazing!"
"This is basic stuff," Muten Natsu said as he took Calpis from the refrigerator and mixed it with ice water. "Didn't they teach this in World of the Living Studies?"
Orihime Inoue accepted the glass from Muten Natsu. "World of the Living Studies?"
"It's a subject at the Shin'ō Academy of Spiritual Arts. Because life in the Soul Society is so different from the World of the Living, it was added about seventy years ago." Rukia Kuchiki took a sip. The icy sweetness was refreshing. "It only covers the bare minimum about the modern world. They wouldn't teach weird problems like filling and draining water at the same time."
Muten Natsu flopped back onto the sofa. "I thought they'd keep up with the times."
"The Shin'ō Academy of Spiritual Arts?" Orihime Inoue sounded intrigued. "So Shinigami have to go to school too..."
Rukia Kuchiki was still battling the math problem while Muten Natsu explained, "It's actually the other way around. Most souls with Reiryoku potential have to study at the Shin'ō Academy before they can become qualified Shinigami."
"Then what do you usually learn there?"
"Basic knowledge about souls, the history of the Soul Society, paperwork, and Zankensoki."
"Zankensoki?"
"The fundamental combat disciplines of the Shinigami," Muten Natsu explained. "Zan refers to fighting with a Zanpakutō. Hakuda is unarmed combat. Hohō covers high-speed movement techniques, such as Shunpo. And Kidō consists of advanced spells used by Shinigami. Kidō is divided into Hadō for destruction, Bakudō for restraint, and Kaidō for healing—like what Rukia used earlier."
"The first few sound fine, kind of like gym class," Orihime Inoue said, tilting her head. "But Kidō sounds really complicated."
"My Kidō grades were excellent~" Rukia Kuchiki said pointedly. "Way better than someone's."
"Huh?" Orihime Inoue looked surprised. "Is Muten's Kidō really that bad?"
"I wouldn't say bad," Muten Natsu replied honestly. "More like terrible. I only know a handful of Bakudō."
Hadō doesn't work well for him, and he can't use healing techniques at all.
"I thought if someone was good at studying, they'd be good at Kidō too," Orihime Inoue said shyly, sticking out her tongue. "Guess Kidō really isn't the same as math."
"They're actually pretty similar," Muten Natsu said after thinking it over. "Solving problems means applying formulas left behind by others using your own logic. Kidō works the same way. You use specially constructed incantations to control your Reiatsu and activate spiritual techniques. Of course, it also involves sensing spiritual fluctuations, manipulating Reishi, and controlling Reiryoku."
"That's exactly why it's unfair," Rukia Kuchiki complained. "We both skip class, and you even sleep during lessons. So why do you always learn this stuff faster than I do?"
"Muten went to junior high before all this," Orihime Inoue said, trying to comfort her. "He already had a foundation, so it's easier for him."
"No, that's not it," Rukia Kuchiki shook her head. "Even back at the Shin'ō Academy, he picked up knowledge faster than I did."
"My Zanpakutō started working back when I was at the academy," Muten Natsu said, tapping his temple. "Simply put, it automatically gathers any knowledge I come into contact with, analyzes it, organizes it, stores it, and then directly gives me whatever information I need."
Orihime Inoue leaned closer to inspect his head. "That's incredible! It's like a computer."
Muten Natsu grinned smugly. "Even better than a computer."
Rukia Kuchiki raised an eyebrow. "And the drawbacks?"
"Huh?" Orihime Inoue immediately imagined Muten Natsu turning into a robot, sparks flying from his head after crashing. "There are drawbacks too?"
"A Zanpakutō's power is a Shinigami's power," Rukia Kuchiki said, staring at him. "An ability this convenient has to come at a cost. So what is it?"
"You've already seen it," Muten Natsu said as he shifted lazily on the sofa. "Laziness."
Muten Natsu lived in full energy-saving mode, diverting everything he conserved straight into his Zanpakutō.
"I can't tell whether you got that kind of Zanpakutō because you're lazy, or if you became this lazy because you have that kind of Zanpakutō." Rukia Kuchiki stared at the math problem in front of her, her expression full of resentment. "But right now, I really am a little jealous of you."
Muten Natsu looked completely serious. "Studying still depends on your own effort. Slacking off isn't a good habit."
Rukia Kuchiki shot him a sideways glare. "You really have the nerve to say that."
"Oh, right." Muten Natsu pushed himself up. "Give me your phone."
"What for?"
"If any more orders come in, I'll handle them myself. You stay at school and attend class properly."
Rukia Kuchiki frowned. "You're going alone?"
"I'll just leave the Gigai in the classroom. I'm usually asleep anyway, so no one will notice." Muten Natsu waved it off. "Your Shinigami powers will take at least two or three months to recover. You should rest properly."
Muten Natsu understood the effects of Soul Essence Stealing all too well.
For a Shinigami who has been subjected to Soul Essence Stealing, the loss of power isn't Reiatsu being used up, but Reiryoku being stripped away.
The former is like physical exhaustion.
The latter is closer to a serious injury.
When you're tired or sleepy, one good rest is enough to recover.
But damage to bones and tendons takes a long time to heal.
Rukia Kuchiki bit her lower lip and tossed the phone over. "Do whatever you want!"
Muten Natsu raised a hand and caught it. Before he could say anything, a command came down from Soul Society.
He slapped his chest lightly, and his soul slipped free of the Gigai. "I'll be right back."
And he really wasn't gone long.
Rukia Kuchiki hadn't even finished a single problem. "Taken care of?"
"No." Muten Natsu returned to his Gigai. "It was just a frightened spirit, a kid. I sent him to Soul Society."
"No Hollows?" Rukia Kuchiki frowned. "That's not good."
Orihime Inoue, who was in the kitchen preparing dinner, asked curiously, "Isn't it a good thing if there were no Hollows?"
Muten Natsu explained, "No Hollows is good. But if a Hollow escaped, that's a different story."
"Hollows usually stay in the space between Soul Society and the World of the Living," Rukia Kuchiki added. "Soul Society can only detect them when they cross the boundary between that space and the World of the Living. This time, an order came down, but no Hollow was found. If it went back into the gap, that's fine. But if it didn't…"
Orihime Inoue followed her reasoning. "Then that means there's a Hollow running around outside Soul Society's surveillance?"
Muten Natsu collapsed face-first onto the sofa. "This is getting troublesome…"