Ryusei returned to his post in the southern reaches of the Land of Hot Water before dawn, the fog still low over the river valleys.
His body moved automatically, but his mind was already somewhere else.
He needed a place, secluded, defensible, and hidden from every faction's eyes.
A laboratory that only he and his chosen few would ever know about.
A small base, nothing large enough to draw attention.
Just enough space for storage seals, a few containment chambers, and workspace for steady, silent progress.
One clone could operate there permanently, maintained with a controlled flow of a fraction of his chakra.
Now that his precision had improved, he no longer had to waste half his reserves each time.
And if danger came, he already had contingencies.
That clone could summon a single fragment of Katsuyu, and then it could reverse summon his true body in seconds.
The slug was turning out to be infinitely more versatile than he had imagined, an ally that could stretch across continents if used properly, an underappreciated game-changer.
Once the site was secure, the plan was simple: guard the place, begin the groundwork, and continue the experiments quietly.
But to set it up right, he needed to study more first.
Orochimaru's notes came to mind.
They were full of raw genius and madness in equal measure, but also structure, a roadmap to building something far beyond conventional shinobi science.
Ryusei would need to immerse himself completely, learn the tools, the techniques, the limitations of chakra-based equipment, and the first logical steps toward independent research.
Eventually, he planned to bring Kanae into it.
Her Byakugan's microscopic precision was perfect for detailed work.
She was also naturally smart, pragmatic, methodical, hungry for research, and unlikely to ever question anything.
The perfect and only direct assistant for all of his future research. Or even the crucial piece.
For that reason, the lab had to be somewhere near enough for her to reach without suspicion, but far enough from prying eyes.
Still, the real centerpiece of his coming research wasn't equipment; it was the treasure he had risked so much to obtain with Pakura.
A true main-branch Byakugan, untainted and pure.
The perfect foundation for what he intended to venture into next.
He was most interested in researching Byakugan right now, after all.
As he stood overlooking the quiet southern forest, the morning mist curling around him, Ryusei's lips curved faintly.
"With this," he thought, "I can start turning theory into power."
"However…" Ryusei muttered, glancing toward the quiet horizon, the morning light just breaking through the mist. "Before all that, I got another idea on the way here."
A grin formed on his face.
He clapped his hands together and summoned a large Katsuyu with a burst of smoke that rippled through the clearing.
The slug materialized in front of him, her enormous, glistening form settling into the grass with a sigh that was half weary, half resigned.
"Ryusei," she said in her calm, echoing voice. "You've been calling me quite often lately… again."
He smirked. "Well, I needed to have a word with my favorite little informant."
Katsuyu's feelers twitched. "Informant?"
"Yes," Ryusei said, crossing his arms. "You know what I'm talking about. The whole… 'snitching to Tsunade' situation. I can't believe you betrayed our professional trust like that. You told on me."
Katsuyu blinked once, slowly. "I report to my primary summoner as part of my duty. She asked that I update her if you ever engaged in suspicious or self-destructive behavior."
Ryusei chuckled. "Suspicious? I was just collecting some samples."
"By forcibly removing them from living hosts," Katsuyu replied, unimpressed. "It caused emotional distress to Lady Tsunade. You should consider that before your next… experiment."
He raised both hands defensively. "You're really committed to this moral oversight role, huh? You know, you're supposed to be neutral."
"I am neutral," Katsuyu replied evenly. "But I prefer not to be summoned into awkward arguments between two humans every other week."
Ryusei laughed quietly. "Fair. Well, relax. I didn't call you here to argue. Actually, I had a new idea."
That made the slug pause, her tone dipping into tired apprehension. "You always say that before I regret appearing."
"This one's different," Ryusei said, his grin widening. "It's about expanding your use in combat. You see, I realized something interesting on the way back."
Katsuyu's antennae twitched again, already sounding unamused. "You mean another 'application' of my biology that Lady Tsunade would strongly disapprove of?"
"Not disapprove," Ryusei said, smirking. "Just never think of. You're wasted on just healing and transport. I realized you could become the core of an entirely new technique, a variation on the Flying Raijin concept - a crawling one to be more exact."
Katsuyu tilted her head slightly. "The unfinished teleportation jutsu of Konoha?"
"Exactly. Think about it," Ryusei said, pacing slowly as he spoke. "I summon you onto the battlefield in your large form. Then you split into countless fragments, scattering across the area. Each fragment becomes a fixed coordinate. Then, using reverse summoning, I can instantly transport myself to any of them. Movement, evasion, repositioning, even attack follow-ups, all instantaneous. I'd be untouchable."
Katsuyu was silent for a few seconds. "You mean to use me as a living network of summoning anchors."
"See?" Ryusei said, grinning wider. "You get it. That's why I like working with you."
Her voice dropped an octave, tired. "You are proposing to weaponize reverse summoning."
"Exactly! Brilliant, right?"
There was another long pause. Then Katsuyu sighed. "You humans always turn cooperation into warfare."
"Oh, come on," Ryusei teased. "It's a genius combination. You're the only creature in existence that can multiply infinitely from one summon. Frogs or snakes would need to summon hundreds individually. You're efficient, one summon, infinite anchors. It's perfect."
Katsuyu didn't respond immediately, her feelers twitching like she was trying to massage away a headache. "This will require immense coordination."
"Already accounted for," Ryusei said confidently. "I can give telepathic orders to your fragments through our link. My sensing precision is strong enough to identify and choose which one I want to jump to instantly. Once we practice enough, it'll be seamless."
Another silence. Then, finally: "Lady Tsunade never made me work this much."
Ryusei grinned. "That's because she didn't see your full potential. You're a hidden masterpiece, Katsuyu. I'm just helping the world appreciate that."
"You are helping me develop back pain," Katsuyu muttered.
Ryusei tilted his head. "What back?"
"The imaginary one I need to carry all your problems."
"Don't be so dramatic," he said, stepping closer and placing a hand on her surface. "Think of it as evolution. When we perfect this, we'll rewrite how summoning and teleportation work together."
Katsuyu let out a low, echoing sigh that made the ground vibrate faintly. "I already regret asking what your idea was."
Ryusei chuckled. "You'll thank me when we pull it off in battle."
And with that, they began testing.
Katsuyu fragmented across the clearing, spreading smaller bodies in a wide radius, while Ryusei experimented with linking, summoning, and instantaneous transfer between them.
To her dismay, and his delight, it worked.
Not flawlessly, not yet, but enough to prove the theory.
Enough to show that they had just created something entirely new.
It actually made perfect sense to Ryusei that this got validated so fast.
After all, the Flying Raijin, in concept, was far closer to ordinary summoning and reverse summoning than to the ordinary Body Flicker or any speed-based technique.
It wasn't about movement at all; it was about displacement, the instantaneous transfer of matter from one point in space to another.
In essence, it operated on the same spatial principles as a summoning jutsu.
Most shinobi misunderstood summoning as something limited to animals, but in truth, it was a far broader art.
Many shinobi summoned inorganic constructs from across the world, objects too large or complex to seal into scrolls.
Summoning Jutsu: Rashomon, for example, was one such case; those massive gates couldn't be stored conventionally, only called through direct spatial summoning.
In that sense, Ryusei's concept wasn't a stretch at all.
The mechanisms greatly overlapped.
By the time they finished, Ryusei stood grinning, his chakra stabilizing after the final jump.
"Perfect," he murmured. "Now we just have to refine it."
Katsuyu sighed again, a ripple running down her massive form. "You are far more exhausting than your predecessor."
Ryusei only laughed. "That's how progress feels. Guess, it's a part of evolution."
The slug's antennae twitched in mild disbelief, but she didn't argue further.
That was how it began, the first step toward 'weaponizing' a slug in Ryusei's words. The start of a partnership so strange it shouldn't have worked, yet would one day reshape battlefields.