Defined by Doujutsu

Today was the 27th day of December, another significant day for those who knew of the future like one Kagami Suguru.

Today was the day that Hinata Hyūga was born.

Watching from the comforts of his own home, Suguru let his eyes bleed crimson as he watched, curious as to how the events he had once only read about, were now coming to life. Moreover, he had grown familiar with these eyes of his, even granting it a name.

[Kaisugan], the Shattered Eyes, since his pupils would shatter and bleed whenever he activated his doujutsu.

"Hm?" Suguru perked up.

Watching yet another wailing infant, Suguru felt an odd pull. Hinata's pure white eyes seemed to draw him in. He felt a familiar yet unfamiliar power flowing into his body. Surprised by the chakra swirling in his eyes, Suguru sat up straight, shocked and alert.

"This..?"

After two whole months, he finally found another lead — a concrete lead at that. 

Suguru seemed to lock eyes with the crying baby. For a moment, Hinata went silent. Hyuga Hiashi, who was guarding the room, grew confused. So did the midwives and Hinata's mother herself.

"Dear, our child has gone silent." She remarked, gently caressing the entranced Hinata in her arms.

Hiashi frowned, having an instinctual feeling that he needed to activate his Byakugan. Blood began to flow, making his arteries swell and supplying his eyes with power. Soon, the world before him turned black, white, and blue.

However, there was nothing abnormal for him to observe. Apart from the excited chakra within Hinata's body, nothing else caught his eye.

"Something's off," He muttered, deactivating his Byakugan. Unfortunately, he could not pinpoint what that off-putting feeling implied.

Thankfully, Hinata no longer seemed distracted. This time, she began looking around with an infant's characteristic gaze. Hiashi's expression softened, and so did everyone else's.

It seemed like the newborn was simply curious about the world she now found herself in. The midwives began cleaning up as they prepared to leave and Hiashi took this opportunity to look at his daughter.

"Hello, Hinata."

He had great expectations for this child of his.

***

"Unfortunately, you'll be disappointed, Hiashi." Suguru chuckled as he pulled his gaze away. Even though he could not hear any distant sounds like a bearer of the Senrigan, he had learned to read lips.

He knew how Hinata would be in the future. Despite the arduous training she would be put through by Hiashi along with Hanabi, she would still prove to disappoint the Hyuga Clan's patriarch.

'I wonder if she'll still be the same now,' Suguru thought as he walked in front of his mirror.

Mirrored back at him is a gaze of pure white. It was a sight he had observed just moments ago. Although blood continued to drip down his cheeks, Suguru could only feel exhilaration.

A cackle escaped his lips. "What kind of eyes do I have?"

The Byakugan had somehow found its way into his hands, seemingly copied by his Kaisugan. 

"No... I think it's more appropriate to say that my eyes have reflected its traits."

With this newfound discovery, Suguru realized he finally had access to his chakra. He nearly jumped in joy!

However, his mind instantly went into its implications. An expression of intrigue appeared on his face as he looked at himself in the mirror.

"When my eyes are in their base states, my chakra becomes an elusive entity, never listening to my commands. However, it seems like this is instead a price I must pay to mirror the special eyes of those around me.

Once I do mirror someone's eyes, that is the only time I can wield my chakra."

Suguru dived deep into his thoughts and began to experiment. He could barely control his excitement.

***

A few hours later, Suguru opened his eyes after a deep meditation. Gone was the pure white Byakugan. What replaced its eerie emptiness was a deep crimson, stained with a black tomoe marking.

Suguru had borrowed a passing Uchiha's Sharingan.

"Hoho," A malicious chuckle. "This is truly unusual. However, I think I now understand my limits."

Suguru couldn't borrow the doujutsu of someone whose eyes were more mature than his. Perhaps that was why, despite gazing into Hyuga Hiashi and Uchiha Fugaku's eyes, he could not mirror their eyes. His Kaisugan had only reacted to Hinata's newly-formed Byakugan and the young Uchiha's single-tomoe Sharingan.

This was quite scientific, in a sense. After all, he only had so much chakra.

Furthermore, Suguru also realized a few other aspects. 

Listing them down, they were as follows:

• His eyes could not 'save' previous eyes that he had mirrored. He would have to look into someone else's eyes to mirror their doujutsu every time he wanted to activate his eyes.

• The stronger the eyes, the more chakra he needed to keep those eyes active. The Sharingan was marginally more taxing, as compared to an inactive Byakugan. Surprisingly, an inactive Byakugan was still classified as a set of eyes he could mirror. Therefore, if he wanted to use his chakra for training in the future, an inactive Byakugan would be the most efficient choice.

• Mirroring the eyes of anyone without a visual Kekkei Genkai achieved nothing aside from changing his eye color. He could not even tap into his chakra. It was a bummer.

• Suguru could only mirror the current state of someone's eyes. In essence, even if he stared into an Uchiha's eyes, as long as the Uchiha did not have their Sharingan activated, then Suguru would gain nothing.

Aside from that, there were a few more things that Suguru wanted to try. For instance, what would happen if he mirrored the eyes of someone right in front of him? What changes would such a situation give him? Would it be more beneficial to do it that way in terms of power?

For now, Suguru didn't know. Moreover, he didn't want to take such a risk... At least not yet.

"I need to test my limits before I dive into unknown waters..."

If people knew that he could somehow copy the Hyuga and Uchiha clan's Kekkei Genkai, then he would be in for quite a bit of trouble. Anyway, his prying abilities were abnormally high. Perhaps it was even better than Hiruzen's crystal ball.

Furthermore, it seemed like no one could sense him doing so, other than those who he could mirror like Hinata and that young Uchiha. Both of them seemed to notice his gaze yet both did not attempt to look away.

In a way, it was similar to Obito's Kamui. While Obito was invulnerable unless he attacked, Suguru was nonexistent until he copied someone's doujutsu.

"At least now, I've figured out how to use chakra for tasks other than using my Kaisugan."

Shaking his head in pleasant surprise, Suguru went to bed. In three days, his parents' funeral ceremony was going to be held.

He felt a weird sense of melancholy at the thought of that.

"To think that even in this life, I would be unable to properly meet those who brought me into the world." A light laugh escaped his lips as he tucked himself into his sheets.

Despite being in a whole new universe, Suguru still wondered what living with a family would be like.