In Naruto with the Flame-Flame Fruit

Among the high-ranking sages of Ryūchi Cave, Ichikishimahime was the most human-like in appearance. Still, she wasn't fond of walking. Floating in the air, she attracted quite the crowd along the way—after all, in the human world, people didn't fly.

Ichikishimahime didn't seem to care. She was endlessly curious about the human world and ended up buying a ton of things… naturally, all paid for with Kiyosuke's money.

After spending the day showing her around and having dinner together, Kiyosuke brought her back to his house.

Ichikishimahime stretched and said with satisfaction,

"Mm… I knew it. Your human world is way more interesting. I got tons of inspiration today."

"Inspiration? For what?"

Kiyosuke raised an eyebrow, curious.

"Of course, inspiration on how to trick humans!" she said brightly. "Last time I couldn't fool you, and we realized… maybe we're falling behind the times. You humans have evolved so fast in recent years. Hardly anyone comes to Ryūchi Cave anymore, so our trials have become ridiculously easy to pass."

Ah. So your trials are just for fun now, huh…

He held his tongue out of politeness, only silently mourning for the next poor soul. Well… as long as it's not him.

He asked, "So, can I start learning how to enter Sage Mode now?"

"Mm, sure. But the natural energy here is way too thin. Let's go back to Ryūchi Cave. Oh, and don't forget to bring back everything I bought!"

"Yeah, yeah, I got it." Kiyosuke packed up all the things she'd picked out into a sealing scroll, then left for Ryūchi Cave with her.

...

The Great White Snake Sage still coiled around the stone table, its massive body almost one with Ryūchi Cave itself. When Kiyosuke arrived, the sage didn't say a word. Instead, Tagitsuhime stepped forward and said,

"Kiyosuke Asakawa, you're here to learn senjutsu, right?"

"Yes. I still haven't figured out how to enter Sage Mode."

Tagitsuhime nodded. "I'll be your guide from now on. Follow us."

"Oh, okay."

He followed behind Tagitsuhime, Ichikishimahime, and the others, entering a pitch-black cave.

Flames lit up the chamber, revealing a stone platform in the center. Tagitsuhime pointed to it and said,

"Go sit up there."

"Alright."

He sat cross-legged on the platform. Tagitsuhime said,

"Now, try to sense the natural energy the Great White Snake Sage left inside your body."

"…I'm not gonna turn into a snake again, am I?" he asked nervously, remembering the pain from last time.

Tagitsuhime shook her head.

"No. Normally, those who try to learn senjutsu at Ryūchi Cave do turn into snakes. If they lose consciousness or fail partway through, we consider it a failure. The truth is, failing to master the Sage Arts at any of the three great lands turns you into one of us."

Just like how failing at Mount Myōboku turns you into a stone toad. Ryūchi Cave just starts the transformation earlier. The process is extremely painful and even a slight mistake can lead to death. It's far more brutal than training at Mount Myōboku or Shikkotsu Forest, though in theory, the entry requirements are a little lower.

In theory, anyway.

Because Kiyosuke already carried natural energy from the Great White Snake Sage, he didn't need to learn how to sense it from scratch. All he had to do was trigger that bit of natural energy inside him, and it would start absorbing more on its own. Eventually, it would become instinctive—his body would draw it in naturally when needed.

Kiyosuke closed his eyes, focusing fully. He carefully searched for that unfamiliar presence inside him. Slowly, his heart calmed… and at last, he sensed it.

Tagitsuhime's voice came through,

"Once you feel it, use your chakra to touch the natural energy."

Following her instructions, Kiyosuke directed his chakra toward the natural energy.

The moment they made contact, it was like an overbearing CEO finding a delicate heroine—his chakra got completely overwhelmed and pulled in, then rapidly fused with the natural energy to become senjutsu chakra. At the same time, his sensitivity to natural energy spiked, and his body began absorbing it more efficiently.

As the fusion progressed, the world around him became sharper in his mind. He could clearly sense where the three sages were positioned. Not only that—he visualized the entire cave in his head, and the range of his perception grew wider and wider. More and more snakes came into view in his mind's eye.

At the corners of his eyes, purple Sage markings appeared—similar to Orochimaru's eyeliner—extending to the sides of his nose. They added a certain mysterious charm to Kiyosuke's already handsome face.

"No signs of snake transformation… a perfect Sage Mode," Tagitsuhime commented.

When Sage Mode isn't perfect, the user's body partially takes on animal traits. For example, Jiraiya's imperfect form made him resemble a toad. Kabuto grew horns during his transformation.

Though… that snake that grew from Kabuto's belly likely had nothing to do with Ryūchi Cave. That was probably just his own personal modification…

Kiyosuke opened his eyes. His formerly round pupils had turned into cold, golden snake eyes. He looked like a refined version of Orochimaru…

"So this is… Sage Mode?"

His body surged with senjutsu chakra. His strength had at least doubled—maybe more.

"Wait… what's this?" He felt something strange in his eyes. When he blinked, a thin transparent film slid over his eyeballs.

"That's a nictitating membrane," Ichikishimahime explained. "Even with perfect Sage Mode, the membrane is part of the package. Now, I'll teach you how to use heat sensing."

Snakes use heat sensors to locate prey through thermal signatures—especially helpful since they're incredibly nearsighted. Ryūchi Cave's snakes had sharp vision, but in a place this dark, heat sensing was essential.

"Oh, that's gonna be super useful."

Especially for the battlefield in Kirigakure, where everyone was obsessed with using thick mist to hide themselves. Heat sensing would be the perfect counter to that.

Kiyosuke picked it up quickly. He hadn't originally possessed the ability, but his previous snake transformation had triggered subtle changes in his body—even ones he didn't notice. The heat sensing system was one of them.

Ichikishimahime simply used senjutsu to activate the ability that had been dormant within him. Best of all, this skill could be used even without entering Sage Mode.

His heat perception worked in a full 360-degree range. In front of him appeared three thermal silhouettes, each in different colors.

"…This is gonna take some getting used to," Kiyosuke muttered. The sensation was unfamiliar, and Ichikishimahime's training now focused on helping him adapt to how he perceived these heat signatures.

"Alright," Tagitsuhime said, "Now comes the senjutsu training. We have a few types here in Ryūchi Cave. I'll explain them, and you can choose three to learn."

It's happening! Time to learn actual senjutsu!

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Pls Drop some Power Stones

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