Book of Sealing

In the center of the wooden cabin, Sakuya and his mentor Obito wore grave expressions as they unfurled the scroll.

The Book of Sealing. A collection of countless forbidden techniques and ninjutsu developed by the Second Hokage, Tobirama Senju. It was nothing short of a treasure trove, which was precisely why Konoha had kept it sealed away for generations.

Deep within the quiet shrine, time seemed to lose all meaning. Only the changing of the seasons outside the window served as a testament to the passage of time.

The massive scroll of the Book of Sealing was slowly spread across the altar, its surface densely packed with the countless forbidden techniques and mysteries collected, developed, and even sealed away since the founding of Konoha. Uchiha Sakuya and Uchiha Obito (in his chakra-consciousness form) sat opposite one another. The mask had been temporarily removed, and two pairs of Sharingan, each harboring different powers and experiences, focused upon this treasury of knowledge and abyss of taboos.

Initial research progressed with alarming smoothness. The power of the Eighty Gods Mirror was nothing short of heaven-defying. Sakuya's eyes acted like a high-efficiency scanner and decoder; those complex, obscure techniques and secret arts that required specific bloodlines or harsh conditions had their core principles and chakra circulation patterns peeled back, understood, and imprinted under his extreme insight and analytical capabilities.

He attempted to replicate the first A-rank ninjutsu: the Shadow Clone Technique. The process was unexpectedly seamless. The light of the Eighty Gods Mirror flowed, completing the analysis and reconstruction of the technique in an instant. Sakuya formed the hand seals, chakra surged—Poof! A clone identical to the original appeared beside him. Success.

Obito observed quietly from the side, his white mask resting on his knees. A flash of admiration crossed his exposed eye, but it was overshadowed by a deep, scrutinizing gaze. He knew that power had never been so cheap.

However, as they ventured deeper into the more forbidden sections of the Book of Sealing, problems began to emerge.

When they attempted to replicate an S-rank genjutsu involving the ultimate application of Yin Release nature transformation, Sakuya clearly felt his chakra consumption increase exponentially! It was not just a matter of quantity, but a qualitative extraction, as if the ocular technique were forcibly squeezing energy from the depths of his soul to complete the process of "reflection" and "reconstruction"!

In the end, although the genjutsu barely took form, Sakuya's face turned pale, and fine beads of cold sweat broke out on his forehead.

"It seems replication is not without its price," Obito said slowly, his voice calm. "The more powerful a technique is, and the more it touches upon the origin of the rules, the heavier the burden on the user. Your Eighty Gods Mirror is more like a bridge, connecting 'understanding' to 'realization,' but the 'toll' required to cross that bridge must still be paid by you."

Sakuya nodded in silence, a hint of gravity flashing in his deep purple eyes (while the Sharingan was inactive). He felt the limitations behind this power.

The true challenge occurred when they first attempted to replicate a fragment of an extremely ancient and dangerous ocular technique recorded at the very end of the Book of Sealing.

It was a forbidden ocular technique involving the tearing of space, its records incomplete and its principles obscure and difficult to grasp.

Sakuya's Eighty Gods Mirror operated at full capacity, the complex patterns in his eyes spinning at an unprecedented speed as he attempted to parse the shattered runes and the distorted flow of chakra. He could feel a massive amount of chakra being frantically drained, even brushing against something deeper—perhaps his life force, or some origin of his soul.

However, just as the model of the ocular technique was about to be completed within his eyes—

Hum!

An extremely unstable, sharp, piercing pain suddenly erupted from the depths of his eyes! It felt as if a mirror were about to shatter!

The ocular technique model under construction instantly became distorted and unstable, then, like shattered glass, it exploded within his "field of vision" and vanished without a trace!

Replication... failed.

A powerful backlash surged back along the connection of the ocular technique. Sakuya let out a muffled groan, his body swaying as his vision went black and a wave of intense nausea washed over him. He felt as if his eyes had been scorched, burning with pain, and his once-plentiful chakra reserves had instantly withered by a significant margin.

More peculiarly, he clearly felt that all the "understanding" and "models" regarding that shattered ocular technique had not disappeared; they still existed in the "records" of the Eighty Gods Mirror, but an invisible "barrier" prevented him from attempting to construct or invoke it again. It was as if his "quota" for the day had been exhausted.

Obito immediately stepped forward, placing a hand on Sakuya's back, slowly channeling gentle yet vast chakra to help him calm the backlash and his chaotic aura.

"Failed, then..." Obito mused. "It seems that even the Eighty Gods Mirror cannot completely defy certain rules. Replicating powerful forces, especially ocular techniques, carries an inherent 'failure rate.' Furthermore, failed techniques seem to be 'locked' for the day, making it impossible to attempt them again."

Over the next year of in-depth research and countless attempts, they gradually grasped the patterns and limitations of the Eighty Gods Mirror's replication ability:

1. Exceptionally high chakra consumption: The chakra consumed to replicate ninjutsu or ocular techniques is far higher than the consumption required to perform the technique after learning it normally, and it is exponentially and positively correlated with the rank of the technique, its complexity, and the level of rules involved. Replicating S-rank or forbidden techniques often drains most of Sakuya's chakra in a single attempt, sometimes requiring Obito's assistance to recover.

2. An inherent failure rate: No matter how thorough the preparation or how deep the analysis, the act of replication by the Eighty Gods Mirror has a basic, unavoidable probability of failure. Through extensive data verification, this probability is stabilized at around forty percent. Failure seems to have a degree of randomness; sometimes replicating a simple A-rank technique fails, while occasionally a hyper-difficult S-rank technique succeeds on the first try.

3. Failure penalty mechanism: Once a replication attempt fails, the model for that ninjutsu or ocular technique enters a "dormant" or "disordered" state for the remainder of the day, making it impossible to attempt replication again. One must wait at least one day for the Eighty Gods Mirror to settle that "disorder" before trying again. This does not guarantee success on the second attempt, as the failure rate persists.

4. Restrictions on ocular techniques are particularly pronounced: The consumption and failure rate for replicating ocular techniques are generally higher than those for ninjutsu of the same rank, especially for Mangekyo-level techniques that require specific bloodlines or extreme emotions to trigger; the failure rate and risk of backlash are extremely high.

This year was a year of rapid growth in power, but also a year of constantly touching boundaries, enduring backlash, and deeply understanding the price of power.

Sakuya mastered a vast number of forbidden techniques and secret arts from the Book of Sealing, reaching an unfathomable level of strength. Yet, he also became more silent, his aura more restrained and dangerous, like a suppressed volcano. Every failed replication and every moment of weakness from drained chakra made him realize more clearly that the Eighty Gods Mirror was not an omnipotent artifact, but a double-edged sword that was extremely sharp yet easily capable of wounding its wielder.

Obito remained by his side, guiding, protecting, and warning him. He watched Sakuya sprint along the path of power, worried that he would be consumed by it, yet understanding that this was a path Sakuya had chosen for himself—a path of no return.

"All power has a price, Sakuya," Obito had warned him once when he was extremely weak after a failed replication. "The Eighty Gods Mirror gives you the 'possibility' to reach all answers, but whether you can actually obtain those answers, and how many you can obtain, still depends on how large and sturdy your own 'vessel' is. Do not let the myriad scenes reflected by this 'mirror' cause you to lose your original heart."

Sakuya merely wiped away the blood seeping from the corner of his eye due to the backlash, his black eyes bottomless.

He knew the price. And he was willing to pay it. As long as this power could help him cut through all the fog and obstacles ahead and complete that final... reckoning. A year of accumulation was enough. The next step of his plan was becoming clear in his mind.

As for Sakuya now, the scope of his expanded ocular techniques alone was enough to rival an entire squad composed exclusively of elite Jonin.

First were the two ocular techniques he was most familiar with and most proficient in using: "Ocular Technique: Kamui" and "Ocular Technique: Amaterasu."

Next were the basic, powerful ocular techniques.

"Ocular Technique: Tsukuyomi," an extremely potent genjutsu.

"Ocular Technique: Kagutsuchi," which could manipulate the form of Amaterasu's flames.

Finally, there was his greatest trump card. It was the strongest control-type ocular technique he had spent an entire month successfully replicating: "Ocular Technique: Kotoamatsukami"!

Putting away the Book of Sealing, Sakuya sat cross-legged on the rooftop, silently practicing the hand gestures for summoning.

This night was destined to be quiet and uneventful. But what would be birthed from countless nights like this would be a monster of terrifying proportions.