Yin Seal

"You're here." Tsunade sat up.

That day, after the Sannin waited for Jiraiya to feel a bit better, they gathered again and talked for a long time.

Finally, Orochimaru came back and told Hyuga Ao to go to Tsunade's place tomorrow.

"Greetings, Tsunade-sama."

"What's with 'Tsunade-sama'? So formal. Call me Tsunade-nee!"

"Alright, Tsunade-nee." Hyuga Ao followed along readily.

Since that day, Tsunade's impression of Hyuga Ao had improved greatly. She skipped the previously mentioned observation period and prepared to help Hyuga Ao implant the Yin Seal.

Tsunade led Hyuga Ao into her tent.

"Strip," Tsunade said.

"Huh?" Hyuga Ao was stunned for a moment.

Tsunade looked at Hyuga Ao's expression and laughed. "Take off your clothes. The Yin Seal requires drawing the formation pattern."

"Oh, oh, oh." Hyuga Ao quickly nodded, but as she undressed, she hesitated.

Even though she was a woman now, whether in this life or her past, she had never undressed in front of another woman.

"Little girl," Tsunade scolded with a smile. "Strip. Nobody's looking at those few scraps of meat you've got."

Hyuga Ao's face reddened. She took off her clothes and knelt on the formation pattern Tsunade had prepared.

Tsunade mixed the ink for drawing the formation pattern, and with one hand, she casually stroked down Hyuga Ao's smooth back, muttering, "Little girl, your skin's pretty nice."

Faced with a female pervert's advance, if she couldn't out-pervert her, Hyuga Ao had no choice but to endure it. Still, that move from Tsunade actually managed to ease Hyuga Ao's awkwardness.

"Relax! Sit up straight! Don't move!" Tsunade's face turned serious as she explained:

"The formation pattern required for the Yin Seal is extremely intricate and complex. The slightest error, and you'll miss by a thousand miles."

"So, while I'm drawing the formation pattern, you absolutely cannot move, understand?"

Hyuga Ao nodded.

After getting Hyuga Ao's confirmation, Tsunade continued:

"Although the Yin Seal only shows externally as a single dot on the forehead, the formation pattern actually covers the entire body."

"We'll draw the upper body pattern first, then the lower body."

"It's actually best to draw the Yin Seal when you're young, because the workload is smallest, and you don't have to shave any hair."

Saying this, Tsunade's expression shifted slightly, as if recalling some painful memory.

"Calm your heart! Focus your mind! I'm starting to draw!" Tsunade said in a low voice.

Hyuga Ao took a deep breath and slowly relaxed her body.

Seeing Hyuga Ao's state, Tsunade nodded in satisfaction and began drawing from Hyuga Ao's forehead.

Hyuga Ao's forehead bore the Caged Bird mark, but that didn't matter—the Caged Bird didn't interfere with applying the Yin Seal.

Tsunade held the brush, its tip touching Hyuga Ao's brow center, and traced downward in one continuous stroke, outlining a face pattern.

Hyuga Ao kept her eyes half-closed, controlling her body not to move.

The special ink Tsunade had mixed felt cool at first on the skin, then slowly began to heat up, until it reached a temperature that brought a slight burning sensation.

Then, a force seemed to emanate from the formation pattern, penetrating beneath the skin, drawing Hyuga Ao's Chakra to flow along the pattern.

Tsunade's brush didn't stop. It slid down along the curve of the neck, swiftly traveling all over the body. After sketching out the rough shape, Tsunade paused the brush and instructed:

"Next, the formation pattern will heat up, and you'll feel a burning sensation. Just endure it, and it'll pass."

After giving Hyuga Ao the warning, Tsunade dipped the brush in more ink and began filling in the details on the front.

Hyuga Ao only felt a coolness on her chest, then cool, cool, cool, cool. She couldn't help opening her eyes and giving Tsunade a reproachful look. Why draw so many strokes there?

Without even lifting her head, Tsunade knew what Hyuga Ao wanted to say. "This is to leave room for the future. The Yin Seal forms a network across the whole body. I'm just worried you might have great potential ahead, and if it snaps, that'd be bad."

Alright, fine. Hyuga Ao could barely accept that explanation.

Just as she resigned herself, Hyuga Ao immediately felt another stroke drawn, and a strange sensation hit her. If she hadn't already reached Embryonic Breathing and had firm control over her body, she would have jolted from the stimulation.

Hyuga Ao helplessly opened her beautiful eyes and stared at Tsunade again, waiting to see how she'd explain this time.

Tsunade put on a serious face and said, "This stroke is to seal the path, and also to connect the upper body network. This spot is the most suitable—it's the convergence point."

"Strange, why didn't she jump up like I did back then?" Tsunade muttered quietly.

But that mutter was just loud enough for Hyuga Ao to hear.

The only part Hyuga Ao could move—her eyes—showed a look of resignation. She simply closed her eyes. Do whatever you want, go ahead.

Tsunade smiled, finished the last few strokes on the front, and then pulled the lines around to the back.

Tsunade dipped the brush in ink again. "The back is the smoothest and most regular, so there's a bit more to draw there. You'll have to endure it. This ink will raise your body temperature all over, then carve the formation pattern into your body, like a tattoo."

"Endure what? Isn't it just some burning sensation?" Hyuga Ao couldn't help wondering.

This kind of thinking from Hyuga Ao only showed she was still young—unfamiliar with this kind of doctor's trick.

The array lines Tsunade drew began to heat up, the warmth linking with Chakra and raising Hyuga Ao's body temperature to nearly 50°C.

Hyuga Ao immediately felt a feverish drowsiness, as if she were trapped inside a furnace. If not for the array lines protecting her body with Chakra, a person would have been dead long ago at this temperature.

After a while.

Hyuga Ao collapsed to the ground. The searing heat from the inscribed array had nearly burned her alive.

Tsunade crouched down and patted Hyuga Ao's cheek. "Wake up. You're not passing out on me already, are you?"

Hyuga Ao pushed herself up and complained in a delicate voice, "Tsunade-sis, you never told me about this before!!!"

"Hahaha." Tsunade burst out laughing. "Next time for sure!"

"Alright, alright. You don't need to get up. Just lie there. I'll finish drawing and we're done."

Hyuga Ao stared wide-eyed at Tsunade. "It's not going to be like that again, is it?"

"No, no. The network's all connected now, and the array's inscribed. Drawing the lower half will be fine."

"Fine." Though she didn't fully trust Tsunade's words, there was no turning back halfway. Hyuga Ao decided to trust her one last time.

The array on her legs was much simpler. The bulk of the work was on her upper body; the legs were just a network for gathering Chakra.

Tsunade quickly finished drawing the legs, sealing the endpoint on Hyuga Ao's sole, linking it through each acupoint, then stopped and put down her brush.

The residual heat traveled along the leg lines to the soles, converging in the acupoint at the arch of the foot, then returning through that point to the internal organs.

Hyuga Ao felt a warm, pleasant sensation in her organs. With that, the entire network across her body was connected. The Yin Seal was mostly complete, with only the final step remaining.

Tsunade formed hand seals, moving at a speed that left afterimages for half a minute.

Finally, Tsunade tapped Hyuga Ao's forehead. The purest trace of Yin Seal Chakra within her spread from the center of Hyuga Ao's brow throughout her body, fully activating the Yin Seal.

With Tsunade's single finger still pressed to Hyuga Ao's forehead, Chakra poured in, and the array lines across Hyuga Ao's body rapidly shrank, all converging into her brow.

Tsunade withdrew her finger, revealing a small diamond-shaped mark on Hyuga Ao's forehead.

"It's done," Tsunade confirmed.

"Hah." Hyuga Ao let out a long breath. Finally over.

Tsunade tossed a scroll to Hyuga Ao. "This covers how to use the Yin Seal. Read it at your leisure. It's not that complicated."

Hyuga Ao dressed, bowed respectfully to Tsunade in thanks, then turned and withdrew.

Stepping out of the tent, Hyuga Ao felt her steps soft and weak, as if she were still recovering from a fever.

She squeezed her fists and stomped her feet. "Strange. Why does my perception feel so much sharper?"

Setting aside her confusion, Hyuga Ao, her whole body limp, slowly shuffled back to her tent.

"The doctor said it'd be quick, that it was nothing—just to distract you! Don't believe it!!!" Hyuga Ao concluded.

Shaking her head, Hyuga Ao returned to her tent and began reading the Yin Seal manual.

The Yin Seal was a Sealing Jutsu created under the leadership of Uzumaki Mito, with the help of the First Hokage and the Second Hokage.

The original idea came from Mito's fear that, given Senju Hashirama's inhuman physique, he might not age while she grew old.

Conceived under that fear, the technique's name used "Yin" to refer to womanhood and also to time itself. The Yin Seal was meant to lock away a woman's passage of time.

She combed through Konoha's secret archives, and with the help of the two Senju brothers, Hashirama and Tobirama, broadened the concept, leading to the Yin Seal as it existed now.

The Yin Seal combined Sealing Jutsu, Medical Ninjutsu, knowledge of the human body, some principles of Kekkei Genkai, and a touch of the essence of Chakra to create it.

Originally, a Yang Seal was meant to accompany the Yin Seal, but the two Senju brothers died too early, so only the Yin Seal remained.

After finishing the introduction, Hyuga Ao followed the instructions and sent the day's remaining Chakra into the Yin Seal. Then, unable to resist the wave of drowsiness crashing over her, she fell into a deep sleep.