Sakura's breasts slapped against her ribcage with a wet clatch as she pulled her dress over her head to wring it dry of river water. What was the endgame here, she wondered to herself as she squirted? She was no closer to finding Obito, and it was only a matter of time before the Hidden Leaf Village discovered that she was the criminal who had styled herself as the Boobie Kid.
"The Inuzuka clan… I was careless," Sakura sighed. "I've never really had much to do with them before, so it never even occurred to me that the village might try to sniff me out using the scent I left behind on my victims…"
Sakura liked to think of herself as someone who saw the big picture, but when one looked at things from so high up, it was easy to miss the trees for the forest. Even though little in the way of superhuman alien blood ran in their veins, and even though they were not particularly powerful, the Inuzuka clan were still at the very top of the niche they occupied.
As Sakura hopped up and down in an effort to peel off her drenched spats, which seemed to have superglued themselves to her massive bottom, she was suddenly overcome with dizziness. She stumbled forwards, clutching her temples as a vicious headache split through her head.
"Ack…! What's… happening to me!?" she gasped. "System!"
Blood flowed freely from her nostrils, dripping from her chin and streaming into the valley of her cleavage. The vertigo worsened, and she toppled backwards onto her ample posterior, feeling as though her brains were liquefying and flowing out through her nose.
[Beep!]
The System's message was lost with another explosion of pain.
Stars burst before her eyes as the encroaching darkness swallowed her sight… but she had not yet lost consciousness. Blinded, she could only listen to the pounding of her own blood rushing in her ears. The only confirmation, aside from her splitting headache, that she was still alive as she sat there, breathing hard…
"Make it… stop!"
…gradually, the pain lessened to a dull ache behind her eyes and nose. Her headache had lessened to the extent that she was once again capable of formulating thoughts.
[Beep! Host… chakra… stop! Moulding… stop!]
After years spent living on the razor's edge as a kunoichi, Sakura had conditioned herself to begin moulding chakra whenever she felt threatened. This was a good thing, as one needed to be able to infuse chakra on the fly in battle, because to stop moving and fighting in the middle of a battle was a death sentence… but in this case, this ingrained reflex proved to be her detriment.
[Beep! The Host's synapses are not yet finished rewiring themselves to accommodate the new sensory stimuli the Host has adapted to receive! The Host must cease moulding chakra, or risk suffering a seizure!]
The last time Sakura had obtained a body-specific Kekkei Genkai, her brain had had plenty of time to adapt. Between obtaining Nanashi's breast chakra and developing her Sharingan, weeks had passed. Furthermore, she had awakened her dōjutsu herself, through her own anger and sadness and feelings of powerlessness; her own chakra had stirred the sinister power slumbering within her pupils.
However, the Byakugan was a completely different story.
Hyūga clan members were born with their iconic pale white eyes already capable of performing their signature dōjutsu; unlike members of the Uchiha clan, who needed to awaken their eyes, with some unable to do so for their entire lives. For Byakugan users, it was simply a matter of learning how to mould chakra and direct it into their eyes to 'activate' them.
(As Kishimoto had initially planned for Himawari to have her mother's eyes but forgot to include them when he drew Chapter 700, I will consider her to have been born with white eyes.)
Just like the Rinnegan or the Rinne Sharingan, the original Byakugan were Kekkei Mōra, and even though the Hyūga's eyes had since degenerated to mere Kekkei Genkai status, they were still considered by most a step above all other dōjutsu in quality, even the Sharingan… amongst the dōjutsu that had survived to the present era, naturally.
Indeed, the Byakugan's ability to see through walls in a three-hundred-and-sixty-degree radius and to perceive objects kilometres away required far greater visuospatial intelligence than any normal human brain was capable of processing. Compared to the Sharingan's Dōsatsugan, the Eye of Insight which expanded the perceivable range of the electromagnetic spectrum and enhanced the user's kinetic and predictive visual acuity, the Byakugan was far more mentally demanding.
All that to say, for Sakura to gain the Hyūga's power, her eyes and brain needed a complete overhaul… but unfortunately for her, or perhaps fortunately, those changes had occurred in the Spiritual Plane, where she was especially vulnerable to having her body altered, and where the flow of time was unnaturally swift. Thus, the adaptation had happened in a single night rather than over the course of weeks or months.
Added to that was the Inuzuka clan's ability to heighten their senses of smell and hearing to the levels of their thoroughbred ninken, which likewise required the brain to forge new connections in order to process an influx of smells and sounds it would ordinarily have no right to perceive… so was it any wonder that Sakura had almost suffered an aneurysm?
For a few seconds, Sakura lay there on the ground, her chest rising and falling with each breath. The instant she had stopped passively moulding chakra, her sight had returned, and her headache had faded away.
"So, that darkness I saw…" she muttered to herself. "I didn't go blind… I was just focusing on somewhere far away…"
Just like a League of Legends player learning to play with an unlocked camera, Sakura had accidentally flicked her mouse slightly and sent her cone of vision flying right off her screen and into the corner of the map… probably somewhere deep beneath her feet, considering how dark it was.
"I already know this is going to be annoying," Sakura sighed.
Just like a baby learning to walk, Sakura was going to have to painstakingly relearn how to see, smell, and hear, or risk being overwhelmed by her own senses. Humans were already an apex species when it came to taste, but now her sight, smell, and hearing had also reached superhuman levels. All she was missing was touch, but seeing as her skin was already highly sensitive, she wasn't missing much.